Trig

Quote:

Originally Posted by xwrathbringerx

http://www.mathhelpforum.com/math-he...9-untitled.bmp

Diagonals = 2 units

(a) Find AD and DC in terms of θ.

(b) Show that DX = sin2θ.

(c) Hence deduce that sin2θ = 2sinθcosθ

Could someone please show me how to start this question? I've been pondering on it for ages.

Hello xwrath..,

$\sin \theta=\frac{DC}{2}$

$\boxed{DC=2\sin \theta}$

$\cos \theta=\frac{AD}{2}$

$\boxed{AD=2\cos \theta}$

$\sin \theta=\frac{DX}{2\cos \theta}$

$\boxed{DX=2\sin \theta \cos \theta}$

$\boxed{\sin 2\theta=2\sin \theta \cos \theta}$

$\boxed{DX=\sin 2\theta}$