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Using Logarithms to Solve Equations

Solve for $x$.

$6^x=216\qquad x=$

$9^x=\frac{1}{3}\qquad x=$

$8^x=16\qquad x=$

What if the bases cannot be made the same? For example, $2^x=7$?

$\textcolor{#17a2b8}{\log}$ to both sides

$2^x=7$

$\textcolor{#17a2b8}{\log}{2^x}=\textcolor{#17a2b8}{\log}{7}$

$\log{2}=\log{7}$

$x=$

$\textcolor{#17a2b8}{\log_a}$ to both sides

$2^x=7$

$\textcolor{#17a2b8}{\log_2}{2^x}=\textcolor{#17a2b8}{\log_2}{7}$

${\log_2}{2}=\log_2{7}$

$=$

$\textcolor{#17a2b8}{\ln}$ to both sides

$2^x=7$

$\textcolor{#17a2b8}{\ln}{2^x}=\textcolor{#17a2b8}{\ln}{7}$

$\ln{2}=\ln{7}$

$x=$

They are are equivalent (you can check on your calculator)

Solve for $x$.

$5\left(4^{2x}\right)=15$

$4^{2x}=$

$\textcolor{#17a2b8}{\log}$ to both sides

$\textcolor{#17a2b8}{\log}{4^{2x}}=\textcolor{#17a2b8}{\log}{3}$

$\log{4}=\log{3}$

$2x=$

$x=$

$\textcolor{#17a2b8}{\log_a}$ to both sides

$\textcolor{#17a2b8}{\log_4}{4^{2x}}=\textcolor{#17a2b8}{\log_4}{3}$

$\log_4{4}=\log_4{3}$

$2x=$

$x=$

$\textcolor{#17a2b8}{\ln}$ to both sides

$\textcolor{#17a2b8}{\ln}{4^{2x}}=\textcolor{#17a2b8}{\ln}{3}$

$\ln{4}=\ln{3}$

$2x=$

$x=$

Solve for $x$.

$2e^{4x-1}-3=7$

$e^{4x-1}=$

$\textcolor{#17a2b8}{\log}$ to both sides

$\textcolor{#17a2b8}{\log}{e^{4x-1}}=\textcolor{#17a2b8}{\log}{5}$

$\log{e}=\log{5}$

$4x-1=$

$x=\;$ / 4

$\textcolor{#17a2b8}{\log_a}$ to both sides

$\textcolor{#17a2b8}{\log_a}{e^{4x-1}}=\textcolor{#17a2b8}{\log_a}{5}$

$\log_a{e}=\log_a{5}$

$4x-1=$

$x=\;$ / 4

$\textcolor{#17a2b8}{\ln}$ to both sides

$\textcolor{#17a2b8}{\ln}{e^{4x-1}}=\textcolor{#17a2b8}{\ln}{5}$

$\ln{e}=\ln{5}$

$4x-1=$

$x=\;$ / 4