Question

(cos9x-cos15x)/(cos6x*sin3x)

Answer 1

$\frac{ - 2 \sin(12x) \sin( - 3x) }{ \cos(6x) \sin(3x) }$
$\frac{4 \sin(6x) \cos(6x) \sin(3x) }{ \cos(6x) \sin(3x) } = 4 \sin(6x)$