Question

find Cos 2A,
cos A= √3/4

Answer 1

Use the following formula:
\[\cos 2A=2\cos ^{2}A-1\]
\[\cos 2A=(2\times (\frac{\sqrt{3}}{4})^{2})-1=you\ can\ calculate\]

Answer 2

cos2A=2cos2A−1 put cos A= √3/4

so cos2A=2*(√3/4)*(√3/4)-1