High School Math : Understanding Negative Exponents

Study concepts, example questions & explanations for High School Math

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Example Questions

Example Question #1 : Exponents

Which of the following is equivalent to \(\displaystyle 3^{-2}\) ? 

Possible Answers:

\(\displaystyle \frac{1}{6}\)

\(\displaystyle -6\)

\(\displaystyle \frac{1}{9}\)

\(\displaystyle -9\)

\(\displaystyle 1\)

Correct answer:

\(\displaystyle \frac{1}{9}\)

Explanation:

By definition, 

\(\displaystyle b^{-x} = \frac{1}{b^{x}}\).

In our problem, \(\displaystyle b = 3\) and \(\displaystyle x = 2\)

Then, we have \(\displaystyle \frac{1}{3^{2}} = \frac{1}{9}\).

Example Question #1 : Negative Exponents

Solve for \(\displaystyle x\):

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

Possible Answers:

\(\displaystyle -5\)

\(\displaystyle -6\)

\(\displaystyle -1\)

\(\displaystyle -4\)

\(\displaystyle -3\)

Correct answer:

\(\displaystyle -6\)

Explanation:

Raise both sides of the equation to the inverse power of \(\displaystyle -3\) to cancel the exponent on the left hand side of the equation.

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

\(\displaystyle \rightarrow x+5 = -1\)

Subtract \(\displaystyle 5\) from both sides:

\(\displaystyle \rightarrow (x+5) - 5 = (-1)-5\)

\(\displaystyle \rightarrow x = -6\)

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