Answer
$\log _{2}a+\log _{2}b-\log _{2}c-\log _{2}d$
Work Step by Step
$\log _{2}\dfrac {ab}{cd}=\log _{2}\left( ab\right) -\log _{2}\left( cd\right) =\log _{2}a+\log _{2}b-\log _{2}c-\log _{2}d
$
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