Trignometric Indentities

Question

Prove the following identity: $4\sin^2x + 7\cos^2x = 4 + 3\cos^2x$

I have no idea where to start on these type of trigonometric identities with the numbers in front of the sin and cos.

Answer 1

$$ 4\sin^2x+7\cos^2x=4\sin^2x+4\cos^2x+3\cos^2x=4+3\cos^2x $$