Question

$Cos\theta +cos3\theta +cos5\theta +cos7\theta =4cos\theta cos2\theta cos4\theta$

• A. True
• B. False

Answer 1

The correct option is A

True

L.H.S. is sum of cos terms and R.H.S. is product of cos terms. To get product from sum, we will apply transformation formula. $\Rightarrow (cos\theta +cos3\theta )+(cos5\theta +cos7\theta )$

$=2cos2\theta cos\theta +2cos6\theta cos\theta )$

$=2cos\theta (cos2\theta +cos6\theta )$

$=2cos\theta 2cos4\theta cos2\theta$

$=4cos\theta cos2\theta cos4\theta$