Rewrite with only sin x and cos x. cos 3x?

the options are

Answer 1

cos(3x) = cos(x + 2x) = cos(x)cos(2x) – sin(x)sin(2x)

= cos(x)(cos²(x) – sin²(x)) – 2sin²(x)cos(x)

= cos(x)(1 – 2sin²(x)) – 2sin²(x)cos(x)

= cos(x) – 4sin²(x)cos(x)

Choose A.

Answer 2

use cos [ a -/+ b ] = cos a cos b +/- sin a sin b and

sin [ a± b ] = sin a cos b ± cos a sin b

{ a }

Leave a Comment