High School Math : Functions and Graphs

Study concepts, example questions & explanations for High School Math

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Example Questions

Example Question #11 : Functions And Graphs

If \(\displaystyle f(x)=3x^{2}+5\) and \(\displaystyle g(x)= x-2\), what is \(\displaystyle g(f(x))\)?

Possible Answers:

\(\displaystyle 3x^{2}+3\)

\(\displaystyle 2x^{2}+5\)

\(\displaystyle 3x^{2}+12x-7\)

\(\displaystyle 3x^{2}-12x+17\)

\(\displaystyle x^{2}-2\)

Correct answer:

\(\displaystyle 3x^{2}+3\)

Explanation:

\(\displaystyle g(f(x))\) means \(\displaystyle f(x)\) gets plugged into \(\displaystyle g(x)\).

Thus \(\displaystyle g(f(x))= (3x^{2}+5) - 2 = 3x^{2}+3\).

Example Question #11 : Functions And Graphs

Let \(\displaystyle f(x)= x^{3}-2x^{2}+x\) and \(\displaystyle g(x)=x^{2}-1\).  What is \(\displaystyle f(g(2))\)?

Possible Answers:

\(\displaystyle 30\)

\(\displaystyle 12\)

\(\displaystyle 48\)

\(\displaystyle 22\)

\(\displaystyle 36\)

Correct answer:

\(\displaystyle 12\)

Explanation:

Calculate \(\displaystyle g(2)\) and plug it into \(\displaystyle f(x)\).

\(\displaystyle g(2)= (2)^{2}-1=4-1=3\)

\(\displaystyle f(3)=(3)^{3}-2(3)^{2}+(3)=27-2(9)+(3)=27-18+3=12\)

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:

\(\displaystyle -30\)

Undefined

\(\displaystyle 196\)

\(\displaystyle 50\)

\(\displaystyle -6\)

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 #1 : Transformations Of Parabolic Functions

If the function \(\displaystyle f(x)\) is depicted here, which answer choice graphs \(\displaystyle f(x+2)\)?

Possible Answers:

C

None of these graphs are correct.

B

Correct answer:
Explanation:

The function \(\displaystyle f(x+b)\) shifts a function f(x) \(\displaystyle b\) units to the left. Conversely, \(\displaystyle f(x-b)\) shifts a function f(x) \(\displaystyle b\) units to the right. In this question, we are translating the graph two units to the left.

To translate along the y-axis, we use the function \(\displaystyle f(x)+k\) or \(\displaystyle f(x)-k\).

Example Question #1 : Understanding Inverse Functions

Let \(\displaystyle f(x)=5-(1+x)^3\). What is \(\displaystyle f^{-1}(x)\)?

Possible Answers:

\(\displaystyle f^{-1}(x)=\left ((5-x)^{3}-1 )\right ^{1/3}\)

\(\displaystyle f^{-1}(x)=\left (1-x)\right ^{1/3}+5\)

\(\displaystyle f^{-1}(x)=(5-x)^{3}-1\)

\(\displaystyle f^{-1}(x)=(5-x)^{\frac{1}{3}}-1\)

\(\displaystyle f^{-1}(x)=\left (1-5x)\right ^{1/3}+1\)

Correct answer:

\(\displaystyle f^{-1}(x)=(5-x)^{\frac{1}{3}}-1\)

Explanation:

We are asked to find \(\displaystyle f^{^{-1}} (x)\), which is the inverse of a function. 

In order to find the inverse, the first thing we want to do is replace f(x) with y. (This usually makes it easier to separate x from its function.).

\(\displaystyle y=5-(1+x)^3\)

Next, we will swap x and y.

\(\displaystyle x=5-(1+y)^3\)

Then, we will solve for y. The expression that we determine will be equal to \(\displaystyle f^{^{-1}} (x)\).

\(\displaystyle x=5-(1+y)^3\)

Subtract 5 from both sides.

\(\displaystyle x-5=-(1+y)^3\)

Multiply both sides by -1.

\(\displaystyle -1(x-5)=5-x=(1+y)^3\)

We need to raise both sides of the equation to the 1/3 power in order to remove the exponent on the right side. 

\(\displaystyle (5-x)^{\frac{1}{3}}=\left ((1+y)^{3} \right )^{1/3}\)

We will apply the general property of exponents which states that \(\displaystyle (a^b)^{c}=a^{b\cdot c}\).

\(\displaystyle (5-x)^{\frac{1}{3}}=\left ((1+y)^{3} \right )^{1/3}=(1+y)^{3\cdot \frac{1}{3}}=(1+y)^1=1+y\)

Laslty, we will subtract one from both sides.

\(\displaystyle (5-x)^{\frac{1}{3}}-1=y\)

The expression equal to y is equal to the inverse of the original function f(x). Thus, we can replace y with \(\displaystyle f^{-1}(x)\).

\(\displaystyle f^{-1}(x)=(5-x)^{\frac{1}{3}}-1\)

The answer is \(\displaystyle f^{-1}(x)=(5-x)^{\frac{1}{3}}-1\).

Example Question #1 : Understanding Inverse Functions

What is the inverse of \(\displaystyle y=4x^{2}\)?

Possible Answers:

\(\displaystyle y=\frac{\pm \sqrt{x}}{2}\)

\(\displaystyle y=\frac{x^{2}}{4}\)

\(\displaystyle y=-4x^{2}\)

\(\displaystyle y=\pm \sqrt{x}\)

\(\displaystyle y=\frac{\pm \sqrt{x}}{4}\)

Correct answer:

\(\displaystyle y=\frac{\pm \sqrt{x}}{2}\)

Explanation:

The inverse of \(\displaystyle y\) requires us to interchange \(\displaystyle x\) and \(\displaystyle y\) and then solve for \(\displaystyle y\).

\(\displaystyle y=4x^{2}\) 

\(\displaystyle x=4y^{2}\)

Then solve for \(\displaystyle y\):

\(\displaystyle y=\frac{\pm \sqrt{x}}{2}\)

Example Question #2 : Understanding Inverse Functions

If \(\displaystyle f(x)=x^{2}+1\), what is \(\displaystyle f^{-1}(x)\)?

Possible Answers:

\(\displaystyle f^{-1}(x)=\frac{1}{x^{2}-1}\)

\(\displaystyle f^{-1}(x)=\frac{1}{x^{2}+1}\)

\(\displaystyle f^{-1}(x)=\sqrt{x-1}\)

\(\displaystyle f^{-1}(x)=\sqrt{x^{2}+1}\)

\(\displaystyle f^{-1}(x)=x^{2}-1\)

Correct answer:

\(\displaystyle f^{-1}(x)=\sqrt{x-1}\)

Explanation:

To find the inverse of a function, exchange the \(\displaystyle x\) and \(\displaystyle y\) variables and then solve for \(\displaystyle y\).

\(\displaystyle x=y^{2}+1\)

\(\displaystyle x-1=y^{2}\)

\(\displaystyle \sqrt{x-1}=y=f^{-1}(x)\)

Example Question #1 : Linear Functions

Which of the following is a horizontal line? 

Possible Answers:

\(\displaystyle y = 0\)

\(\displaystyle y=2x+1\)

\(\displaystyle y = -x\)

\(\displaystyle y = 3x + 4\)

\(\displaystyle x = 4\)

Correct answer:

\(\displaystyle y = 0\)

Explanation:

A horizontal line has infinitely many values for \(\displaystyle x\), but only one possible value for \(\displaystyle y\). Thus, it is always of the form \(\displaystyle y = c\), where \(\displaystyle c\) is a constant. Horizontal lines have a slope of \(\displaystyle 0\). The only equation of this form is \(\displaystyle y = 0\)

Example Question #1 : Linear Functions

Which of the following is a vertical line? 

Possible Answers:

\(\displaystyle x = 3\)

\(\displaystyle y = \frac{1}{x}\)

\(\displaystyle y = 4\)

\(\displaystyle y = x\)

\(\displaystyle y = 3x + 2\)

Correct answer:

\(\displaystyle x = 3\)

Explanation:

A vertical line is one in which the \(\displaystyle y\) values can vary. Namely, there is only one possible value for \(\displaystyle x\), and \(\displaystyle y\) can be any number. Thus, by this description, the only vertical line listed is \(\displaystyle x = 3\)

Example Question #13 : Functions And Graphs

Which of the following has a slope of 0? 

Possible Answers:

\(\displaystyle x = 0\)

\(\displaystyle y = x\)

\(\displaystyle y = 10\)

\(\displaystyle y = \frac{1}{x}\)

\(\displaystyle y = 3^{x}\)

Correct answer:

\(\displaystyle y = 10\)

Explanation:

A line with a slope of zero will be horizontal. A horizontal line has only one possible value for \(\displaystyle x\), and \(\displaystyle y\) can be any value. 

Thus, the only given equation which fits this description is \(\displaystyle y = 10\).

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