We know how to find 2^{-1}. But what about 2^{-2}, 2^{-3},2^{-4},\ldots ?

To work out {\color{blue}{2}}^{{\color{red}{-2}}}, all we need to do is find the reciprocal of the base ({\color{blue}{2}}) and then raise that reciprocal to the same power but with the opposite sign ({{\color{red}{+2}}}) .

\begin{align} {\color{blue}{2}}^{\color{red}{-2}} &=\left(\dfrac{1}{{\color{blue}{2}}}\right)^{\color{red}{2}} \\[5pt] &=\left(\dfrac{1}{{\color{blue}{2}}}\right)\times \left(\dfrac{1}{{\color{blue}{2}}}\right) \\[5pt] &=\left(\dfrac{1\times 1}{{\color{blue}{2}}\times{\color{blue}{2}}}\right) \\[5pt] &=\dfrac{1}{4}. \end{align}

A similar approach can be used for other powers. Let's see another example.

FLAG

Evaluate 2^{-3}.

EXPLANATION

We find the reciprocal of the base ({\color{blue}{2}}), and then raise that reciprocal to the same power but with the opposite sign ({{\color{red}{+3}}}), as follows:

\begin{align} {\color{blue}{2}}^{\color{red}{-3}} &=\left(\dfrac{1}{{\color{blue}{2}}}\right)^{\color{red}{3}}\\[5pt] &=\left(\dfrac{1}{2}\right)\times \left(\dfrac{1}{2}\right)\times \left(\dfrac{1}{2}\right)\\[5pt] &=\left(\dfrac{1\times 1\times 1}{2\times2\times2}\right) \\[5pt] &=\dfrac{1}{8} \end{align}

FLAG

$3^{-2}=$

a
$-\dfrac {1} {9}$
b
$-9$
c
$-6$
d
$\dfrac {1} {9}$
e
$9$

$(-3)^{-3}=$

a
$-\dfrac{1}{27}$
b
$\dfrac{1}{9}$
c
$-9$
d
$-\dfrac{1}{9}$
e
$27$

$2^{-4} =$

a
$ \dfrac 1 {16}$
b
$\dfrac 1 {8}$
c
$-\dfrac 1 {16}$
d
$- \dfrac 1 {32}$
e
$-\dfrac 1 {8}$

Calculate the value of \left(\dfrac{1}{4}\right)^{-2}.

EXPLANATION

We find the reciprocal of the base \left(\dfrac 1 4\right), and then raise that reciprocal to the same power but with the opposite sign (+{\color{blue}2}), as follows:

\begin{align} \left(\dfrac{1}{4}\right)^{-\color{blue}2} &=(4)^{\color{blue}2} \\[5pt] &=4\cdot 4 \\[5pt] &=16 \end{align}

FLAG

$\left(\dfrac{1}{9}\right)^{-2}=$

a
$-\dfrac{1}{81}$
b
$-\dfrac{1}{18}$
c
$-\dfrac{17}{9}$
d
$18$
e
$81$

$\left(\dfrac 1 2\right)^{-3}=$

a
$8$
b
$-8$
c
$\dfrac 1 6$
d
$-\dfrac 1 8$
e
$\dfrac 1 8$

$\left(\dfrac 1 2\right)^{-4}=$

a
$16$
b
$32$
c
$\dfrac{1}{16}$
d
$8$
e
$\dfrac{1}{8}$

Express \dfrac {1} {49} as a base raised to a negative exponent.

EXPLANATION

First, we write \dfrac{1}{49} as a base raised to a power: \begin{align*} \dfrac {1} {49} &= \dfrac{1 \times 1}{7 \times 7} \\[5pt] &= \dfrac{1}{7} \times \dfrac{1}{7} \\[5pt] &= \left( \dfrac{1}{7} \right)^2 \end{align*}

Now, we find the reciprocal of the base \left(\dfrac{1}{7}\right), and then raise that reciprocal to the same power but with the opposite sign (-2), as follows:

\left( \dfrac{1}{7} \right)^2 = 7^{-2}

FLAG

Express $\dfrac {1} {25} $ as a base raised to a negative exponent.

a
$2^{-5}$
b
$-5$
c
$-\dfrac{1}{25}$
d
$ -5^{2}$
e
$ 5^{-2}$

Express $\dfrac {9} {4} $ as a base raised to a negative exponent.

a
$-\left(\dfrac23\right)^{2}$
b
$\left(\dfrac23\right)^{-2}$
c
$\left(\dfrac32\right)^{-2}$
d
$\left(\dfrac23\right)^{2}$
e
$-\left(\dfrac23\right)^{-2}$

Express $\dfrac {8} {125} $ as a base raised to a negative exponent.

a
$-\left(\dfrac 52\right)^{-3}$
b
$\left(\dfrac 25\right)^{-3}$
c
$\left(\dfrac 52\right)^{-3}$
d
$\left(\dfrac 52\right)^{3}$
e
$-\left(\dfrac 25\right)^{3}$
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