Question

(cos9x-cos15x)/(cos6x*sin3x)

Answer 1

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