Question

Tunjukan bahwa : (cos 2x + cos 4x + cos 6x) sinx = sin3x.cos4x , tolong pakai cara lengkap ya, makasiii

Answer 1

(cos2x + cos4x + cos6x) sinx
= (cos4x + cos6x + cos2x) sinx
= (cos4x + 2 cos(6x+2x)/2 . cos(6x-2x)/2) sinx
= (cos4x + 2 cos 4x cos2x) sinx
= cos4x (1 + 2cos2x) sinx
= cos4x (sinx + 2cos2x sinx)
= cos4x (sinx + sin(2x+x) - sin(2x-x))
= cos4x (sinx + sin3x - sin x)
= sin3x cos4x