Finding inverse functions (ACT). Game on.

Finding inverse functions (ACT) is a grade 11 math skill aligned to Common Core standard HSF.BF.B.4.a. Below are 8 practice questions with answers and step-by-step explanations, drawn from the 10 finding inverse functions (act) problems our math games drill.

CCSS HSF.BF.B.4.a10 questions in the bank
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Warm-upmedium

Given f(x)=x35f(x)=x^{3}-5, which of the following is f1(x)f^{-1}(x)?

Set y=x35y=x^{3}-5. Swap: x=y35x=y^{3}-5. Add 55: x+5=y3x+5=y^{3}. Take the cube root: y=x+53y=\sqrt[3]{x+5}. So f1(x)=x+53.f^{-1}(x)=\sqrt[3]{x+5}\textsf{.}

Mid-gamemedium

If f(x)=4x+13f(x)=\sqrt[3]{4x+1}, then f1(x)=f^{-1}(x)=

Set y=4x+13y=\sqrt[3]{4x+1}. Swap: x=4y+13x=\sqrt[3]{4y+1}. Cube both sides: x3=4y+1x^{3}=4y+1. Subtract 11 and divide by 44: y=x314y=\dfrac{x^{3}-1}{4}. So f1(x)=x314.f^{-1}(x)=\dfrac{x^{3}-1}{4}\textsf{.}

Mid-gamemedium

Which expression represents the inverse of f(x)=x+2f(x)=\sqrt{x+2}?

Set y=x+2y=\sqrt{x+2}. Swap: x=y+2x=\sqrt{y+2}. Square both sides: x2=y+2x^{2}=y+2. Subtract 22: y=x22y=x^{2}-2. So f1(x)=x22.f^{-1}(x)=x^{2}-2\textsf{.}

Mid-gamemedium

The inverse of f(x)=3x1f(x)=\dfrac{3}{x-1} is

Set y=3x1y=\dfrac{3}{x-1}. Swap: x=3y1x=\dfrac{3}{y-1}. Multiply: x(y1)=3x(y-1)=3. Divide by xx: y1=3xy-1=\dfrac{3}{x}. Add 11: y=3x+1y=\dfrac{3}{x}+1. So f1(x)=3x+1.f^{-1}(x)=\dfrac{3}{x}+1\textsf{.}

Mid-gamemedium

If f(x)=2x3+1f(x)=2x^{3}+1, which of the following equals f1(x)f^{-1}(x)?

Set y=2x3+1y=2x^{3}+1. Swap: x=2y3+1x=2y^{3}+1. Subtract 11: x1=2y3x-1=2y^{3}. Divide by 22: x12=y3\dfrac{x-1}{2}=y^{3}. Take the cube root: y=x123y=\sqrt[3]{\dfrac{x-1}{2}}. So f1(x)=x123.f^{-1}(x)=\sqrt[3]{\dfrac{x-1}{2}}\textsf{.}

Mid-gamemedium

What is f1(x)f^{-1}(x) when f(x)=7xf(x)=7-x?

Set y=7xy=7-x. Swap: x=7yx=7-y. Solve for yy: y=7xy=7-x. So f1(x)=7x.f^{-1}(x)=7-x\textsf{.}

Mid-gamemedium

Given f(x)=2x+35f(x)=\dfrac{2x+3}{5}, which expression is f1(x)f^{-1}(x)?

Set y=2x+35y=\dfrac{2x+3}{5}. Swap: x=2y+35x=\dfrac{2y+3}{5}. Multiply by 55: 5x=2y+35x=2y+3. Subtract 33: 5x3=2y5x-3=2y. Divide by 22: y=5x32y=\dfrac{5x-3}{2}. So f1(x)=5x32.f^{-1}(x)=\dfrac{5x-3}{2}\textsf{.}

Buzzer beatermedium

If f(x)=(x4)3f(x)=(x-4)^{3}, then f1(x)=f^{-1}(x)=

Set y=(x4)3y=(x-4)^{3}. Swap: x=(y4)3x=(y-4)^{3}. Take the cube root: x3=y4\sqrt[3]{x}=y-4. Add 44: y=x3+4y=\sqrt[3]{x}+4. So f1(x)=x3+4.f^{-1}(x)=\sqrt[3]{x}+4\textsf{.}

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