Fill the blank on the right side with a simple trigonometric

Fill the blank on the right side with a simple trigonometric expression and prove that the resulting equation is an identity.

Simplify.

(cos 4x - cos6x)/(sin4x+sin6x)

cosA-cosB=-2sin(A+B)/2 Sin(A-B)/2

Sin A+SIn B=2sin(A+B)/2 cos(A-B)/2

-2sin(4x+6x)/2 sin (4x-6x)/2/ 2sin (4x+6x)/2 cos(4x-6x/2)

2sin5x sinx/ 2sin 5xcosx

sinx/cosx=tanx