Precalculus : Piecewise Functions

Study concepts, example questions & explanations for Precalculus

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Example Questions

Example Question #1 : Piecewise Functions

Let

\(\displaystyle y=\left\{\begin{matrix} 2x&x\leq 0\\ x+9& x>0 \end{matrix}\right.\)

What does \(\displaystyle y\) equal when \(\displaystyle x=3\)?

Possible Answers:

\(\displaystyle 6\)

\(\displaystyle 3\)

\(\displaystyle 10\)

\(\displaystyle 12\)

Correct answer:

\(\displaystyle 12\)

Explanation:

Because 3>0 we plug the x value into the bottom equation.

\(\displaystyle x=3\)

\(\displaystyle y=x+9\)

\(\displaystyle y=3+9=12\)

Example Question #1 : Piecewise Functions

Let

\(\displaystyle y=\left\{\begin{matrix} x-9&x\leq 0\\ x+9& x>0 \end{matrix}\right.\)

What does \(\displaystyle y\) equal when \(\displaystyle x=0\)?

Possible Answers:

\(\displaystyle 8\)

\(\displaystyle 0\)

\(\displaystyle -9\)

\(\displaystyle 9\)

Correct answer:

\(\displaystyle -9\)

Explanation:

Because \(\displaystyle 0\leq0\) we use the first equation.

\(\displaystyle y=x-9\)

Therefore, plugging in x=0 into the above equation we get the following,

\(\displaystyle y=0-9=-9\).

Example Question #1 : Piecewise Functions

Determine the value of \(\displaystyle f(1)\) if the function is

\(\displaystyle f(x)=\left\{\begin{matrix} x& x< 3\\ \pi&x=3 \\ 4&x>3 \end{matrix}\right.\)

Possible Answers:

\(\displaystyle f(1)=1\)

\(\displaystyle f(1)=3\)

\(\displaystyle f(1)=4\)

\(\displaystyle f(1)=\pi\)

Correct answer:

\(\displaystyle f(1)=1\)

Explanation:

In order to determine the value of \(\displaystyle f(1)\) of the function we set \(\displaystyle x=1.\) 

The value comes from the function in the first row of the piecewise function, and as such

\(\displaystyle f(1)=1\)

Example Question #1 : Piecewise Functions

Determine the value of \(\displaystyle f(1)\) if the function is

\(\displaystyle f(x)=\left\{\begin{matrix} \sqrt{x}& 0\leq x< 4\\ \3&x=4 \\ e^{-x}&x>4 \end{matrix}\right.\)

Possible Answers:

\(\displaystyle f(1)=\frac{1}{e}\)

\(\displaystyle f(1)=3\)

\(\displaystyle f(1)=1\)

\(\displaystyle f(1)=3\)

Correct answer:

\(\displaystyle f(1)=1\)

Explanation:

In order to determine the value of \(\displaystyle f(1)\) of the function we set \(\displaystyle x=1.\) 

The value comes from the function in the first row of the piecewise function, and as such

\(\displaystyle f(1)=\sqrt{1}=1\)

Example Question #1 : Piecewise Functions

For the function \(\displaystyle f(x)\) defined below, what is the value of \(\displaystyle f(x)\) when \(\displaystyle x=3\)?

\(\displaystyle f(x)=\left\{\begin{matrix} -x+1&\text{ for }x< 1\\ x^{2}-2&\text{ for }1< x< 3\\ 2^{x}&\text{ for }x\geq 3 \end{matrix}\)

Possible Answers:

7

-2

0

8

3

Correct answer:

8

Explanation:

Evaluate the function for \(\displaystyle x=3\). Based on the domains of the three given expressions, you would use \(\displaystyle 2^{x}\), since \(\displaystyle x\) is greater than or equal to \(\displaystyle 3\).

\(\displaystyle 2^{x}=2^{3}=8\)

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