Algebra II : Function Notation

Study concepts, example questions & explanations for Algebra II

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Example Questions

Example Question #1 : Function Notation

Let \displaystyle f(x)=2-2x+x^2 and \displaystyle g(x)=2x-1. What is \displaystyle f(g(x))?

Possible Answers:

\displaystyle 2x^3-5x^2+6x-2

\displaystyle 4x^2-8x+5

\displaystyle 4x^2-4x+5

\displaystyle 2x^2-4x+3

\displaystyle x^2+3

Correct answer:

\displaystyle 4x^2-8x+5

Explanation:

THe notation \displaystyle f(g(x)) is a composite function, which means we put the inside function g(x) into the outside function f(x). Essentially, we look at the original expression for f(x) and replace each x with the value of g(x).

The original expression for f(x) is \displaystyle 2-2x+x^2. We will take each x and substitute in the value of g(x), which is 2x-1.

\displaystyle f(g(x))=f(2x-1)

\displaystyle =2-2(2x-1)+(2x-1)^2

\displaystyle =2-2(2x-1)+(2x-1)^2

We will now distribute the -2 to the 2x - 1.

\displaystyle 2-4x+2+(2x-1)^2

We must FOIL the \displaystyle (2x-1)^2 term, because \displaystyle (2x-1)^2=(2x-1)(2x-1)

\displaystyle 2-4x+2+(2x-1)^2=2-4x+2+(2x-1)(2x-1)

\displaystyle =2-4x+2+4x^2-2x-2x+1

Now we collect like terms. Combine the terms with just an x.

\displaystyle 2+2+4x^2+1-8x

Combine constants.

\displaystyle 4x^2-8x+5

The answer is \displaystyle 4x^2-8x+5.

Example Question #22 : How To Find F(X)

Solve the function for \displaystyle x. When \displaystyle f(x)=16

What does \displaystyle x equal when, \displaystyle f(x)=16

\displaystyle f(x)=x^{2}-9

Possible Answers:

\displaystyle \pm5

25

-5

0

\displaystyle \sqrt{5}

Correct answer:

\displaystyle \pm5

Explanation:

Plug 16 in for \displaystyle f(x).  \displaystyle 16=x^2-9

Add 9 to both sides.  \displaystyle x^2=25

Take the square root of both sides. \displaystyle \sqrt{25}=\displaystyle \sqrt{x^{2}}

Final answer is \displaystyle x= \displaystyle \pm5

Example Question #1 : Function Notation

Evaluate \displaystyle \small f(g(3)) if \displaystyle f(x)=6x-4 and \displaystyle g(x)=x^2.

Possible Answers:

Undefined

\displaystyle -30

\displaystyle 50

\displaystyle 196

\displaystyle -6

Correct answer:

\displaystyle 50

Explanation:

\displaystyle \small f(g(3))

This expression is the same as saying "take the answer of \displaystyle \small g(3) and plug it into \displaystyle \small f(x)."

First, we need to find \displaystyle \small g(3). We do this by plugging \displaystyle \small 3 in for \displaystyle \small x in \displaystyle \small g(x).

\displaystyle g(x)=x^2

\displaystyle g(3)=3^2=9

Now we take this answer and plug it into \displaystyle \small f(x).

\displaystyle f(g(3))=f(9)

We can find the value of \displaystyle \small f(9) by replacing \displaystyle \small x with \displaystyle \small 9.

\displaystyle f(x)=6x-4

\displaystyle f(9)=6(9)-4=50

This is our final answer.

Example Question #2 : Function Notation

Orange Taxi company charges passengers a $4.50 base fase, plus $0.10 per mile driven. Write a function to represent the cost of a cab ride, in terms of number of miles driven, \displaystyle x.

Possible Answers:

\displaystyle f(x) = 4.5^x

\displaystyle f(x) = 0.1 + 4.5x

\displaystyle f(x) = x + 4.5^x

\displaystyle \displaystyle f(x) = 4.5 + 0.1x

\displaystyle f(x) = 4.5 + 1^x

Correct answer:

\displaystyle \displaystyle f(x) = 4.5 + 0.1x

Explanation:

Total cost of the cab ride is going to equal the base fare ($4.50) plus an additional 10 cents per mile. This means the ride will always start off at $4.50. As the cab drives, the cost will increase by $0.10 each mile. This is represented as $0.10 times the number of miles. Therefore the total cost is:

\displaystyle f(x) = 4.5 + 0.1x

Example Question #2 : Function Notation

A small office building is to be built with \displaystyle 2 long walls \displaystyle y feet long and \displaystyle 4 short walls \displaystyle x feet long each. The total length of the walls is to be \displaystyle 150 feet.

Write an equation for \displaystyle y in terms of \displaystyle x.

Possible Answers:

\displaystyle y = 150 - 4x

\displaystyle y = 75 - 2x

\displaystyle y = 2x - 75

\displaystyle y = 2x + 150

Correct answer:

\displaystyle y = 75 - 2x

Explanation:

The pre-question text provides us with all of the information required to complete this problem. 

We know that the total length of the walls is to be \displaystyle 150 ft.

We also know that we have a total of \displaystyle 2 y walls and \displaystyle 4x walls.

 

With this, we can set up an equation and solve for \displaystyle y.

Our equation will be with sum of all the walls set equal to the total length of the wall...

\displaystyle 2y + 4x = 150

Remeber, we want \displaystyle y in terms of \displaystyle x, which means our equation should look like

\displaystyle y= something

 

\displaystyle 2y + 4x = 150  Subtract \displaystyle 4x on both sides

\displaystyle 2y = 150 - 4x  Divide by \displaystyle 2 on both sides

\displaystyle 2y/2 = (150-4x)/2   Simplify

\displaystyle y = 75 - 2x     Answer!!!

Example Question #2 : Function Notation

What is the slope of the function \displaystyle f(x)= -5x+3?

Possible Answers:

\displaystyle \frac{3}{5}

\displaystyle -\frac{5}{3}

\displaystyle 3

\displaystyle x

\displaystyle -5

Correct answer:

\displaystyle -5

Explanation:

The function is written in slope-intercept form, which means:

\displaystyle y = mx+b

where:

\displaystyle m= slope

\displaystyle x= x value

\displaystyle b= y-intercept

Therefore, the slope is \displaystyle {\color{Red} -5}

Example Question #2 : Function Notation

A cable company charges a flat $29.99 activation fee, and an additional $12.99 per month for service.  How would a function of the cost be represented in terms of months of service, \displaystyle x?

Possible Answers:

\displaystyle f(x)=41.98x

\displaystyle f(x)=12.99 +29.99x

This cannot be written as a function

\displaystyle f(x)=17x

\displaystyle f(x)=29.99+12.99x

Correct answer:

\displaystyle f(x)=29.99+12.99x

Explanation:

\displaystyle f(x)= 29.99+12.99x

The flat rate of 29.99 does not change depending on months of service.  It is $29.99 no matter how long services are in use.  The monthy fee is directly related to the number of months the services are in use.

Example Question #5 : Function Notation

Find \displaystyle f(3) for the following function:

\displaystyle f(x)=\frac{4x+3}{x^2}

Possible Answers:

\displaystyle \frac{5}{3}

\displaystyle 15

\displaystyle 3

\displaystyle \frac{12x+9}{x^2}

\displaystyle 9

Correct answer:

\displaystyle \frac{5}{3}

Explanation:

To evaluate \displaystyle f(3), we just plug in a \displaystyle 3 wherever we see an \displaystyle x in the function, so our equation becomes

\displaystyle f(3)=\frac{3\cdot 4+3}{3^2}

which is equal to

 \displaystyle f(3)=\frac{5}{3}

Example Question #7 : Function Notation

Find \displaystyle f(g+h) for the following function:

\displaystyle f(x)=cos(5x^2)e^x

Possible Answers:

\displaystyle cos(5g^2)e^{g}+cos(5h^2)e^{h}

\displaystyle cos(5g^2e^{g})+cos(5h^2e^{h})

\displaystyle cos(5g^2+5h^2)e^{g+h}

\displaystyle cos(5g^2+10gh+5h^2)e^{g+h}

\displaystyle cos(5g^2+10gh+5h^2)e^{g}+e^h

Correct answer:

\displaystyle cos(5g^2+10gh+5h^2)e^{g+h}

Explanation:

To find \displaystyle f(g+h), all we do is plug in \displaystyle (g+h) wherever we see an \displaystyle x in the function. We have to be sure we keep the parentheses. In this case, when we plug in \displaystyle (g+h), we get

\displaystyle cos(5(g+h)^2)e^{g+h}

Then, when we expand our binomial squared and distribute the \displaystyle 5, we get

\displaystyle cos(5g^2+10gh+5h^2)e^{g+h}

Example Question #2 : Function Notation

If \displaystyle f(x)=g(x)-3, and  \displaystyle g(x)=x^{2} -1, for which of the following \displaystyle x value(s) will \displaystyle f(x) be an odd number?

Possible Answers:

\displaystyle 7

\displaystyle 2

\displaystyle 4

\displaystyle -2

\displaystyle -6

Correct answer:

\displaystyle 7

Explanation:

First, x needs to be plugged into g(x).

Then, the resulting solution needs to be substituted into f(x).

For example,

\displaystyle g(7) = 49-1 = 48

\displaystyle f(7) = g(7)-3 = 48-3 = 45

Since 45 is an odd number, 7 is an x value that gives this result. Because both equations subtract an odd number to get the final result, only an odd number will result in an odd result therefore, none of the other options will give an odd result.

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