# Thread: Proving something is equal to tan x

1. ## Proving something is equal to tan x

$(sin 2x + sin x) / (cos 2x + cos x+1) = tan x$

2. Originally Posted by nerdzor
$(sin 2x + sin x) / (cos 2x + cos x+1) = tan x$
Substitute the double angle formula into the left hand side:

$\sin(2x) = 2 \sin x \cos x$

$\cos (2x) = 2 \cos^2 x - 1$

Simplify. Factorise. Cancel the common factor. Viola!