The Total solution for NCERT class 6-12
Consider
LHS = cos 4x
We can write it as
= cos 2(2x)
Using the formula cos2A┬а= 1 тАУ 2 sin2┬аA
= 1 тАУ 2 sin2┬а2x
Again by using theformula sin2A┬а= 2sin┬аA┬аcos┬аA
= 1 тАУ 2(2 sin┬аx┬аcos┬аx)┬а2
So we get
= 1 тАУ 8 sin2x┬аcos2x
= R.H.S.