which is an irrational number

Which Is An Irrational Number

Answers

Answer 1

Answer:

The irrational number is [tex]\sqrt{\frac{5}{3}}[/tex].

__________________________________

Definition : In mathematics, the irrational numbers are all the real numbers which are not rational numbers. That is, irrational numbers cannot be expressed as the ratio of two integers.

Answer 2

Answer:

Step-by-step explanation:

I'm not sure but I think it's A

I'm not sure!!

(pls do not vote ..)

Bye!


Related Questions

Write the phrase as an algebraic expression and simplify if possible. Let x represent the unknown number

Three times a number, decreased by five

(Simplify your answer.)

Answers

EZ,
3x-5
(3x) = 3 times a number.
Decrease means subtract.

To express the phrase "Three times a number, decreased by five" as an algebraic expression, we can use the variable x to represent the unknown number: 3x - 5

Now, let's simplify this expression: Given that the unknown number is represented by x, we can substitute it into the expression above. Substituting x into the expression, we have: [tex]3(x) - 5 3x - 5[/tex] Therefore, the algebraic expression representing "Three times a number, decreased by five" is [tex]3x - 5.[/tex] At this point, there is no further simplification possible since the expression is already in its simplest form.

For example, let's assume the unknown number x is 7. We can plug in this value to evaluate the expression: [tex]3(7) - 5 = 21 - 5 = 16[/tex] Similarly, if x is -2, the calculation would be: [tex]3(-2) - 5 = -6 - 5 = -11[/tex] In conclusion, the algebraic expression 3x - 5 represents the phrase "Three times a number, decreased by five."

To know more about algebraic expression visit:

https://brainly.com/question/953809

#SPJ2

Is 69 square routed a even number

Answers

No it is not, the square root is 8.3

look at attachment below

Answers

I think it’s 8/55=4/x
So it’s 8x=4(55)
8x=220
x=220/8
x=27.5

subtract

a2-b2 from a2 +b2

Answers

Answer:

2b^2

Step-by-step explanation:

according to the question equation is

(a^2 + b^2 ) - (a^2 - b^2)

a^2 + b^2 - a^2 + b^2

plus a square and minus a square gets cancel

b^2 + b^2

since they are like terms they can be added

2b^2

Answer:

2b^2

Step-by-step explanation:

according to the question equation is

(a^2 + b^2 ) - (a^2 - b^2)

a^2 + b^2 - a^2 + b^2

= b^2 + b^2

like terms can be added

+2b^2

Expand, and simplify the following expressions a. (2x+y)(x+y) + (2x-y)(x+y)​

Answers

Step-by-step explanation:

2x²+2xy+yx+y²+2x²+2xy-yx+y²

2x²+2x²+2xy+2xy+yx-yx+y²+y²

2x²+2x²+2xy+2xy

4x²+4xy

Your Answer is in the above image.

Hope this solution may help you

An educational psychologist wondered whether there was a relationship between the amount of academic pressure a high school student felt and their plans for college. They surveyed a random sample of 300 high school students throughout the country about their college plans and whether they felt academic pressure. Here are the responses and partial results of a chi-square test (expected counts appear below observed counts):
Chi-square test:
Planned years of college vs. feeling academic pressure now
O years Up to 4 years Up to 4 years More than 4 years Total
Yes 31 48 161 240
31.2 48 160.8
No 8 12 40 60
7.8 12 40.2
Total 39 60 201 300
They want to use these results to carry out a xạ test of independence. Assume that all conditions for inference were met. What are the values of the test statistic and P-value for their test?
What are the values of the test statistic and P-value for their test?
A. x² = 0.002;
0.001 < P-value < 0.0025
B. x² = 0.002;
P-value > 0.25
C. x² = 0.007;
0.005 < P-value < 0.01
D. x² = 0.007;
P-value > 0.25

Answers

Answer:

D. x² = 0.007;

P-value > 0.25

Step-by-step explanation:

The observed and expected values are given below :

Yes____31 48 161 ____240

______31.2 48 160.8

No ____ 8 12 40_____ 60

______7.8 12 40.2

Total __ 39 60 201 ___300

The Chisquare statistic, χ²:

Σ(Observed - Expected)²/ Expected

Chi-Squared Values:

0.00128205 __ 0 __ 0.000248756

0.00512821 __ 0 __ 0.000995025

(0.00128205 + 0 + 0.000248756 + 0.00512821 + 0 + 0.000995025 )

= 0.007654041

The degree of freedom = (row - 1) * (column - 1)

Degree of freedom = (2-1)*(3-1) = 1*2= 2

The Pvalue = 0.9962

Pvalue > 0.25

PLS HELP

the simplest form of this product has a numerator of

x + 2
x - 2
( x - 2 ) ( x - 2 )
( x + 2 ) ( x - 2 )

and a denominator of

x - 5
( x - 5 ) ( x - 1 )
x - 1
( x + 5 ) ( x + 1 )

the expression has an excluded value of x

- 5
2
-1
5

Answers

(x+2)(x-2) / (x-1)(x-5) this is the simplified form of the expression.

What is fraction?

A fraction is a mathematical term that represents a part of a whole or a ratio between two quantities. It is a way of expressing a number as a quotient of two integers, where the top number is called the numerator, and the bottom number is called the denominator.

x²-3x-10/x²-6x+5 • x-2/x-5

We can factor the numerator and denominator of the first fraction as follows: (x-5)(x+2) / (x-5)(x-1)

Notice that there's a common factor of x-5 in both the numerator and denominator. We can cancel them out, leaving: (x+2) / (x-1)

Now let's simplify the second fraction:

x-2 / x-5

We can't simplify this fraction any further, so we leave it as is.

Putting it all together, we get:

(x+2) / (x-1) * (x-2) / (x-5)

Multiplying the two fractions, we get:

(x+2)(x-2) / (x-1)(x-5)

This is the simplified form of the expression.

To learn more about fraction from the given link:

https://brainly.com/question/10354322

#SPJ1

I need help with this!

Answers

Answer:

1.  y=5   x=1

2.  y=4   x=4/5

3.  y=2   x=2/5

Step-by-step explanation:

Plug the y-values in for y:

1. 5=5x

2. 4=5x

3. 2=5x

Then solve for x:

1. x=1

2. x=4/5

3. x= 2/5

Hope this helps!

WILL GIVE BRAINLIEST Solve for x

Answers

Answer:

Step-by-step explanation:

sin x° = [tex]\frac{17}{19}[/tex]

x° = [tex]sin^{-1}[/tex] [tex]\frac{17}{19}[/tex]

x° ≈ 63°

After being rejected for employment, Kim Kelly learns that the Bellevue Credit Company has hired only four women among the last 19 new employees. She also learns that the pool of applicants is very large, with an approximately equal number of qualified men as qualified women.
Help her address the charge of gender discrimination by finding the probability of getting four or fewer women when 19 people are hired, assuming that there is no discrimination based on gender.
(Report answer accurate to 8 decimal places).
P(at most four) =

Answers

Answer:

P(at most four) = 0.00960541

Step-by-step explanation:

For each employee hired, there are only two possible outcomes. Either it is a women, or it is not. The probability of an employee being a women is independent of any other employee, which means that the binomial probability distribution is used to solve this question.

Binomial probability distribution

The binomial probability is the probability of exactly x successes on n repeated trials, and X can only have two outcomes.

[tex]P(X = x) = C_{n,x}.p^{x}.(1-p)^{n-x}[/tex]

In which [tex]C_{n,x}[/tex] is the number of different combinations of x objects from a set of n elements, given by the following formula.

[tex]C_{n,x} = \frac{n!}{x!(n-x)!}[/tex]

And p is the probability of X happening.

19 new employees.

This means that [tex]n = 19[/tex]

Approximately equal number of qualified men as qualified women.

This means that [tex]p = 0.5[/tex]

Probability of getting four or fewer women when 19 people are hired

This is:

[tex]P(X \leq 4) = P(X = 0) + P(X = 1) + P(X = 2) + P(X = 3) + P(X = 4)[/tex]

In which

[tex]P(X = x) = C_{n,x}.p^{x}.(1-p)^{n-x}[/tex]

[tex]P(X = 0) = C_{19,0}.(0.5)^{0}.(0.5)^{19} = 0.00000191[/tex]

[tex]P(X = 1) = C_{19,1}.(0.5)^{1}.(0.5)^{18} = 0.00003624[/tex]

[tex]P(X = 2) = C_{19,2}.(0.5)^{2}.(0.5)^{17} = 0.00032616[/tex]

[tex]P(X = 3) = C_{19,3}.(0.5)^{3}.(0.5)^{16} = 0.00184822[/tex]

[tex]P(X = 4) = C_{19,4}.(0.5)^{4}.(0.5)^{15} = 0.00739288[/tex]

Then

[tex]P(X \leq 4) = P(X = 0) + P(X = 1) + P(X = 2) + P(X = 3) + P(X = 4) = 0.00000191 + 0.00003624 + 0.00032616 + 0.00184822 + 0.00739288 = 0.00960541[/tex]

So

P(at most four) = 0.00960541

what is 1+1+3+4+6+2+6+3+5=+8+2+5

Answers

Answer:

16

Step-by-step explanation:

baámmáy tính  

A man, 1.5m tall, is on top of a building. He observes a car on the road at an angle of 75°. If the building is 30m, how far is the car from the building?​

Answers

Answer:

The answer to this question is 8.44 m.

Step-by-step explanation:

This problem is best illustrated in the photo below.

First, we must know that the angle stated in the problem is the angle of depression. Angle of depression is the angle between the horizontal and the line of sight of the observer. On the other hand, if the observer is looking upward, then the angle between the horizontal and his line of sight is called the angle of elevation.

Since we have the given angle of depression, we must use its complementary angle to solve for the distance of the car from the building.

Let x = complementary angle of 75°

y = distance of the car from the building

To solve for x,

To solve for y, we need to use a trigonometric function that will relate the adjacent of 15° and the opposite of 15°. Let us look at the mnemonics

SOH: Sine =  

CAH: Cosine =  

TOA: Tangent =  

Therefore we must use the tangent function to solve for y.

 

There is a bag filled with 3 blue and 4 red marbles.
A marble is taken at random from the bag, the colour is noted and then it is replaced.
Another marble is taken at random.
What is the probability of getting exactly 1 blue?

Answers

Answer:

its a three in seven chance, since there are seven total outcomes and there is only one favorable outcome. Hope that helps.

Step-by-step explanation:

DO THIS FAST PLEASE I WILL GIVE BRAINLY CROWN



Use a model to divide. 5 ÷ 1/2 10 4 2 20

Answers

5 ÷ 1/2 => 5 x 2/1 => 10/1 => 10

Answer:

10

Step-by-step explanation:

In the pic, it shows ten half squares.  

What is the volume in cubic centimeters of the figure below?

Answers

Answer:

so that you will multiply 15 * 4.

Step-by-step explanation:

15*4 = 60 now you divide 60 by 4 and the answer will be 15.

I need help please anyone

Answers

The answer is a or d u choose

Answer:

20

Step-by-step explanation:

l*w*h

4*5*1= 20

1.) If I am selling a dozen at $3, how much would each egg cost?
2.) If each egg costs that amount of money, how much would an 18 pack be?


I'm trying to figure this out because this is a real-life problem, and I'm trying to sell eggs to my teacher.

Answers

Answer:

1.$3÷12=0.25

each egg would cost 25 cents

2.12×18=216

216×25=5,400

What is 15 5/7 - 6 4/5

Answers

Answer:

8.9

Step-by-step explanation:

15.71428571-6.8=8.914285714

We round of to one significant figure because its addition n the lowest is 6.8

Answer:

[tex]8\frac{32}{35}[/tex]

Step-by-step explanation:

Which of the following represents the factorization of the trinomial below?
x2 - 14x + 49
O A. (x-7)
O B. (x-7)(x+7)
O C. (x+7)
O D. (x+2)(x+7)
ANSWER ASAP!!

Answers

the answer should be B!

[tex]\implies {\blue {\boxed {\boxed {\purple {\sf { \: ( {x - 7})^{2} }}}}}}[/tex]

[tex]\large\mathfrak{{\pmb{\underline{\red{Step-by-step\:explanation}}{\red{:}}}}}[/tex]

[tex] {x}^{2} - 14x + 49[/tex]

[tex] = {x}^{2} - 7x - 7x + 49[/tex]

Taking "[tex]x[/tex]" as common from first two terms and "7" from last two terms, we have

[tex] = x \: ( \: x - 7 \: ) - 7 \: ( \: x - 7 \: )[/tex]

Taking the factor [tex](x-7)[/tex] as common,

[tex] = ( \: x - 7\:) \: (\: x - 7\: )[/tex]

[tex] =( {x - 7})^{2} [/tex]

[tex]\large\mathfrak{{\pmb{\underline{\orange{Mystique35 }}{\orange{❦}}}}}[/tex]

write the other side of this equation so its true for all values of x: 1/2(6x-10)-x=

Answers

9514 1404 393

Answer:

  2x -5

Step-by-step explanation:

Any equivalent expression can be used. It is perhaps easiest just to simplify the given expression.

  1/2(6x -10) -x = 3x -5 -x = 2x -5

Putting 2x-5 on the right will give an equation true for all x.

  1/2(6x -10) = 2x -5

Classify each differential equation as separable, exact, linear, homogeneous, or Bernoulli. Some equations may be more than one kind. Do not solve.
a) dy/dx = (x − y)/x
b) (x + 1)dy/dx = −y + 20
c) dy/dx = 1/(x(x − y2))
d) dy/dx =(y^2 + y)/(x^2 + x)
e) dy/dx = 5y + y^2
f) y dx = (y − xy^2) dy
g) x dy/dx = ye^(xy) − x
h) 2xyy' + y^2 = 2x^2
i) y dx + x dy = 0
k) (x^2 + 2y/x) dx = (3 − ln x^2) dy
l) (y/x^2) dy/dx + e^(2x^3) + y^2 = 0

Answers

a) dy/dx = (x − y)/x=> This is a separable differential equation.b) (x + 1)dy/dx = −y + 20=> This is a linear first-order differential equation.c) [tex]dy/dx = 1/(x(x - y^2))[/tex]=> This is a separable differential equation.d) [tex]dy/dx = (y^2 + y)/(x^2 + x)[/tex]=> This is a separable differential equation.e)[tex]dy/dx = 5y + y^2[/tex]=> This is a Bernoulli differential equation.f) [tex]y dx = (y - xy^2) dy[/tex]=> This is a separable differential equation.g) [tex]x dy/dx = ye^{(xy)} - x[/tex] => This is a linear first-order differential equation.h) [tex]2xyy' + y^2 = 2x^2[/tex]=> This is a linear first-order differential equation.i) y dx + x dy = 0 => This is a separable differential equation.k) [tex](x^2 + 2y/x) dx = (3 - \text ln x^2) dy[/tex] => This is a linear first-order differential equation.l) [tex](y/x^2) dy/dx + e^{(2x^3)} + y^2 = 0[/tex] => This is a linear first-order differential equation.

Here, we have to classify each differential equation based on their characteristics:

a) dy/dx = (x − y)/x

This is a separable differential equation because the variables can be separated on different sides of the equation.

It's of the form dy/dx = g(x) - f(y)/h(y), where g(x) = x/x and h(y) = 1.

b) (x + 1)dy/dx = −y + 20

This is a linear first-order differential equation because it can be rearranged to the form y' + P(x)y = Q(x), where P(x) = -1/(x + 1) and Q(x) = 20/(x + 1).

c) [tex]dy/dx = 1/(x(x - y^2))[/tex]

This is a separable differential equation because the variables x and y can be separated on different sides of the equation.

d) [tex]dy/dx = (y^2 + y)/(x^2 + x)[/tex]

This is a separable differential equation because the variables x and y can be separated on different sides of the equation.

e)[tex]dy/dx = 5y + y^2[/tex]

This is a Bernoulli differential equation because it is of the form [tex]dy/dx = p(x)y + q(x)y^n[/tex], where p(x) = 0 and q(x) = 5x, n = 2.

f) [tex]y dx = (y - xy^2) dy[/tex]

This is a separable differential equation because the variables x and y can be separated on different sides of the equation.

g) [tex]x dy/dx = ye^{(xy)} - x[/tex]

This is a linear first-order differential equation because it can be rearranged to the form y' + P(x)y = Q(x), where P(x) = -1/x and [tex]Q(x) = e^{(xy)} - x^{(-1)[/tex].

h) [tex]2xyy' + y^2 = 2x^2[/tex]

This is a linear first-order differential equation because it can be rearranged to the form y' + P(x)y = Q(x), where P(x) = -2/x and Q(x) = 2x.

i) y dx + x dy = 0

This is a separable differential equation because the variables x and y can be separated on different sides of the equation.

k) [tex](x^2 + 2y/x) dx = (3 - \text ln x^2) dy[/tex]

This is a linear first-order differential equation because it can be rearranged to the form y' + P(x)y = Q(x), although it's not immediately obvious what P(x) and Q(x) are.

l) [tex](y/x^2) dy/dx + e^{(2x^3)} + y^2 = 0[/tex]

This is a linear first-order differential equation because it can be rearranged to the form y' + P(x)y = Q(x), where [tex]P(x) = -1/x^2[/tex] and [tex]Q(x) = -e^{(2x^3)} - y^2[/tex].

To know more about differential equation, visit:

brainly.com/question/1164377

#SPJ12

The ice cream man just ended his shift for the day. Let 1/2x^2 6/11x + 8 represent the amount of chocolate ice cream bars he sold. Let 5/9x^2 + 2/3 represent the amount of vanilla ice cream bars he sold. Finally let 1/3x^2 + 4x + 4/3 represent the amount of strawberry ice cream bars he sold. Select all the statements that are true

a. The total amount of ice cream bars sold can be represented by the expression 25/18x^2+ 50/11x +10
b. The total amount of ice cream bars sold can be represented by the expression 25/18x^2 + 172/33x +28/3
c. He sold 1/6x^2 + 50/11x + 28/3 more chocolate than strawberry ice cream bars.
d. He sold 1/6x^2 - 38/11x + 20/3 more chocolate than strawberry ice cream bars.

Answers

Answer:

A and D

Step-by-step explanation:

Total ice cream bars sold = sum of chocolate sold , vanilla and strawberry ice-creams sold.

=(1/2)x2 + (6/11)x + 8 + (5/9)x2 + (2/3) +(1/3)x2 + 4x +(4/3) (Given in the question)

=(25/18)x2 + (50/11)x + 10 (Adding terms corresponding to x2,x ,constant respectively)

Difference in chocolate and strawberry bars =[ (1/2)x2 + (6/11)x + 8] - [(1/3)x2 + 4x +(4/3)]

= (1/6)x2 - (38/11)x +(20/3)

So, the correct options are A and D

Which function is increasing and has a domain of (1,∞ )

Answers

The graph of a square root function has a domain of (0, ∞) and range of [1, ∞).

Answer:

f(x)=log(x-1)+2

Step-by-step explanation:

I did the test on plato and got it right.

Simplify
x×x×x×у×у and
2×x×x×3×y×y×y​

Answers

Step-by-step explanation:

1.x³y²

2. 6x²y³

hope it helps

Construct a frequency polygon that represents the following data regarding the selling prices of houses sold in 2006 for a particular neighborhood find the midpoint

Class Frequency
78787 – 98786 9
98787 – 118786 8
18787 – 138786 9
138787 – 158786 4
158787 – 178786 8

Answers

Answer:

See attachment for polygon

Step-by-step explanation:

Given

[tex]\begin{array}{cc}{Class} & {Frequency} & 78787 - 98786 & 9 &98787 - 118786 & 8 & 118787 - 138786 & 9 & 138787 - 158786 & 4 & 158787 - 178786 & 8 \ \end{array}[/tex]

Required

The frequency polygon

First, we calculate the midpoint of each class.

This is the average of the class limits

So, we have:

[tex]x_1 = \frac{78787 + 98786}{2} = \frac{177573}{2} = 88786.5[/tex]

[tex]x_2 = \frac{98787 + 118786}{2} = \frac{217573}{2} = 108786.5[/tex]

----

--

-

[tex]x_5 = \frac{158787 + 178786}{2} = \frac{337573}{2} = 168786.5[/tex]

(138787 + 158786)/2

So, the table becomes:

[tex]\begin{array}{ccc}{Class} & {Frequency} & {x} &78787 - 98786 & 9 & 88786.5 & 98787 - 118786 & 8 & 108786.5 & 118787 - 138786 & 9 & 128786.5 & 138787 - 158786 & 4 & 148787.5 & 158787 - 178786 & 8 & 168786.5\ \end{array}[/tex]

See attachment for frequency polygon

A crew clears brush from 1/3 acre of land in 2 days. How long will it take the same crew to clear the entire plot of 2 1/ 2 acres?

Answers

Answer:

15 days

Step-by-step explanation:

Given that :

Time taken to clear 1/3 acre = 2 days

This means that, they will be able to clear ;

1/3 ÷ 2 = 1/3 * 2 /1 = 1/6 acre in one day

1/6 acres per day :

Hence, the number of days it will take to clear 2 1/2 acres will be :

2 1/2 acres ÷ 1/6

5 / 2 ÷ 1/ 6

5/2 * 6 /1 = (5*6) / (2*1) = 30/2 = 15

Hence, it will take 15 days to clear 2 1/2 acres

Diana is going to roll a 6-sided die. What's the probability she will role a 4 or
a 5? *

Answers

The probability of rolling any one number on a 6 sided die is 1/6

The probability of rolling a 4 is 1/6

The probability of rolling a 5 is 1/6

The probability of rolling a 4 or a 5 is the probability of rolling a 4 plus the probability of rolling a 5:

1/6 + 1/6 = 2/6 = 1/3

The answer is 1/3

Find Length of x line OR

Answers

ATQ:-

Both figures r similar (given )

so :-

[tex] \frac{5}{2.5} = \frac{3}{1.5} = \frac{2}{1} = \frac{4}{x} \\ \frac{2}{1} = \frac{4}{x} \\ \frac{ \cancel{2}}{1} = \frac{ \cancel{4}^ { \tiny{2}}}{x} \\ x = 2 \: \: ans[/tex]

Có 7 cây hãy trồng thành 6 hàng, mỗi hàng 3 cây?

Answers

Answer:

Step-by-step explanation:

Bạn vẽ 1 tức giác ABCD lồi sau đó nối AB và CD cắt nhau tại E, AD và BC cắt nhau tại F, AC và BC cắt nhau tại G. Trồng 7 cây vào các điểm ABCDEFG  l. Ta có sáu hàng là ABE, DCE, BCF, ADF, ACG, BDG

The interarrival time of nuclear particles in a Monte Carlo simulation of a reaction is designed to have a uniform distribution over an interval from 0 to 0.5 milliseconds. Determine the probability that the interarrival time between two particles will be:

Answers

Answer:

Incomplete question, but you can use the formulas given to solve it.

Step-by-step explanation:

Uniform probability distribution:

An uniform distribution has two bounds, a and b.

The probability of finding a value of at lower than x is:

[tex]P(X < x) = \frac{x - a}{b - a}[/tex]

The probability of finding a value between c and d is:

[tex]P(c \leq X \leq d) = \frac{d - c}{b - a}[/tex]

The probability of finding a value above x is:

[tex]P(X > x) = \frac{b - x}{b - a}[/tex]

Uniform distribution over an interval from 0 to 0.5 milliseconds

This means that [tex]a = 0, b = 0.5[/tex]

Determine the probability that the interarrival time between two particles will be:

Considering [tex]a = 0, b = 0.5[/tex], and the question asked, you choose one of the three formulas above.

Other Questions
Please help Ill give brainliest how are humans different from each other? I need help Ill mark u as brainlest Anyone plz plz answer Why did UN coalition troops battle Iraqi forces in 1991? Find the area of each shape, please help and I will give a lot points Which of the following situations would a local government address? Presidential electionTrade with other nationsSupport of armed forcesDamaged streetlights Which graph shows the solution to the equation 4x-4=4? I NEED THIS ASAAPPbrudbdjdbhsbdhd please help steps thx NWC, NWH, and NWV are three firms that dominate the water distribution market. Identify this type of market structure and compare it to perfect competition. The circumference of a circle is 16Pi ft.The radius is ____ ft. The vertex of this parabola is at (-2,-3). When the y-value is -2, the x-value is -5. What is the coefficient of the squared term in the parabola's equation? 5 re (-2, -3) Two sides of an isosceles triangle are unknown. We can say both are X ftlong each. The third side is 9 ft long. Perimeter of the triangle is 33ft. Whatis the length of each missing side? A. 10B. 11C. 12D. 9 how to raise awareness of water pollution around your school?? this is due date in 14h so today this is primarily for edenuity 2020-21 :) What is traditional economic system? "HOT PIZZA" is offering a 20% discount on all its pizzas.Sam orders a pizza for the reduced price of 5.60What was the original price of the pizza? explain face what that photo express I need help please.Q: which of the following is correct reference entry for a book in APA format.