Question

If Cos²x = 1/3, then cos4x=?

Answer 1

Formula of cos 4x, ie you need the angle in x form…

Since, we know cos 2x = cos²x - sin²x & sin2x = 2sinxcosx

By applying the above..

So, cos 4x

= cos 2*2x

= cos² 2x - sin² 2x

= ( cos 2x)² - (sin 2x)²

= ( cos²x - sin²x )² - (2sinx*cosx)²

= cos^4 x + sin^4 x- 2sin²x.cos²x - 4 sin²x*cos² x

= cos^4(x) + sin^4(x) - 6 sin²xcos²x

PS! Since Formula is asked. It can be expressed in the t- ratios of any reduced angle form….

Answer 2

hope its help

i have applied only one formula here

that is cos 2x = 2cos^2x - 1

and have a good day