Mathematics

Problem

Given

\sin 2\theta = \dfrac{4}{5}

and

\theta

is acute with

\sin \theta < \cos \theta

, find

\cos \theta

. a)

\dfrac{1}{\sqrt{5}}

\sqrt{\dfrac{2}{5}}

\dfrac{2}{\sqrt{5}}

\dfrac{\sqrt{21}}{5}