Question

Question #88d71

Answer 1

Proven

Explanation:

`cos4x = cos(2x+2x)`
`cos4x = cos^(2)2x-sin^(2)2x`
`cos4x = 1-sin^(2)2x-sin^(2)2x`
`cos4x = 1-2sin^(2)2x`
`cos4x = 1-2(2sinxcosx)^2`
`cos4x = 1-2(4sin^2xcos^2x)`
`cos4x = 1-8sin^2xcos^2x`