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Laws of Logarithms

Adding Logarithms

$\log_2{4}+\log_2{8}=\quad$ $\log_2{12}\qquad$   $\log_2{16}\qquad$   $\log_2{32}\qquad$   $\log_4{8}\qquad$   $\log_8{4}$    

$\log_3{1}+\log_3{27}=\quad$ $\log_3{28}\qquad$   $\log_3{27}\qquad$   $\log_3{81}\qquad$   $\log_1{27}\qquad$   $\log_27{3}$    

$\log_5{\frac{1}{5}}+\log_5{25}=\quad$ $\log_5{5}\qquad$   $\log_5{25}\qquad$   $\log_5{25\frac{1}{5}}\qquad$   $\log_{25}{\frac{1}{5}}\qquad$   $\log_{25}{5}$    

$\log_4{2}+\log_4{8}=\quad$ $\log_4{\frac{1}{4}}\qquad$   $\log_4{2}\qquad$   $\log_4{8}\qquad$   $\log_4{10}\qquad$   $\log_4{16}$    

The examples follow the rule,
$\log_a{x}+\log_a{y}=\quad$ $\log_a{\left(x+y\right)}\qquad$   $\log_a{\left(x-y\right)}\qquad$   $\log_a{\left(xy\right)}\qquad$   $\log_a{\left(x^y\right)}$    


Let's investigate why $\log_2{4}+\log_2{8}=\log_2{\left(32\right)}$.

Let $4=2^m$. Then $m=$

Let $8=2^n$. Then $n=$

$\log_2{\left(32\right)}=\log_2{\left(4\times8\right)}=\log_2{\left(2^2\times2^3\right)}=\log_2{\bigl(2}$$2+$ $\bigl)=2+3=\log_2{4}+\log_2{8}$


Let's investigate why $\log_a{x}+\log_a{y}=\log_a{\left(xy\right)}$.

$\log_a{\left(x \times y\right)}=\log_a{\Bigl(a^{\log_a{}}}$ $\times a$ $\Bigl)=\log_a{\Bigl(a}$ $\Bigl)=\log_a$ $+\log_a$

Subtracting Logarithms

$\log_2{16}-\log_2{8}=\quad$ $\log_2{1}\qquad$   $\log_2{2}\qquad$   $\log_2{4}\qquad$   $\log_2{8}\qquad$   $\log_2{16}$    

$\log_3{81}-\log_3{27}=\quad$ $\log_3{1}\qquad$   $\log_3{\frac{4}{3}}\qquad$   $\log_3{3}\qquad$   $\log_3{9}\qquad$   $\log_3{54}$    

$\log_5{5}-\log_5{25}=\quad$ $\log_5{\left(-20\right)}\qquad$   $\log_5{\frac{1}{5}}\qquad$   $\log_5{\frac{1}{25}}\qquad$   $\log_5{\frac{1}{125}}\qquad$   $\log_5{5}$    

$\log_4{2}-\log_4{16}=\quad$ $-\log_4{\left(8\right)}\qquad$   $\log_4{\left(-14\right)}\qquad$   $\log_4{\frac{1}{4}}\qquad$   $\log_4{\frac{1}{8}}\qquad$   $\log_4{\frac{1}{16}}$    

The examples follow the rule,
$\log_a{x}-\log_a{y}=\quad$ $\log_a{\left(x+y\right)}\qquad$   $\log_a{\left(x-y\right)}\qquad$   $\log_a{\left(xy\right)}\qquad$   $\log_a{\left(\frac{x}{y}\right)}$    


Let's investigate why $\log_3{81}-\log_3{27}=\log_3{3}$.

Let $81=3^m$. Then $m=$

Let $27=3^n$. Then $n=$

$\log_3{\left(3\right)}=\log_3{\left(\frac{81}{27}\right)}=\log_3{\left(\frac{3^4}{3^3}\right)}=\log_3{\Bigl(3}$$4-$ $\Bigl)=4-3=\log_3{81}-\log_3{27}$


Let's investigate why $\log_a{x}-\log_a{y}=\log_a{\left(\frac{x}{y}\right)}$.

$\log_a{\left(\frac{x}{y}\right)}=\log_a{\Biggl(}$ $a$ / $a$ $\Biggl)=\log_a{a}$ $=\log_a$ $-\log_a$

If possible, use the laws of logarithms to simplify and write as a single logarithm or rational number.
If it is not possible, type “simplified“.

$\frac{\log{7}}{\log{3}}$

$\log{4}+\log{7}$

\left(\log 2\right)\left(\log 5\right)

$\log{m}-\log{n}$

$\frac{1}{\log 5}$

$\left(\log x\right)\left(\log y\right)$

$\left(\log{x}\right)^p$

$\log{\left(a+b\right)}$

$\log{\left(2+x\right)}$

$\frac{\log{y}}{\log{x}}$

$\left(\log{5}\right)^2$

$\frac{1}{\log x}$

$\frac{\log{81}}{\log{27}}$

$\left(\log{3}\right)^2$

$p\log{x}+q\log{y}$

$\frac{\log{64}}{\log{16}}$

$-\log{x}-\log{y}$

$2\log{3}+3\log{2}$

$\log{56}-\log{8}$

$\frac{\log{14}}{\log{2}}$

$-\log{24}-\log{3}$

$-\log{8}-\log{2}$

$\log{4}+3\log{2}$

$\frac{\log{25}}{\log{125}}$

$\log{p}-\log{q}$

$\log{x}+\log{y}$

$\log{\left(y+3\right)}$

$\log{\left(x-y\right)}$

$2\log{3}+\log{5}$

$\log{a}+\log{b}$

$\log{\left(m-n\right)}$

$\log{2}+\log{3}$

$\log{\left(x-4\right)}$

$\log{18}-\log{2}$