# Good ol' trigonometry (KVPY)

Geometry Level 4

$\large \csc^2 (a+b) - \sin^2 (b-a) + \sin^2 (2a-b) = \cos^2 (a-b)$

The equation above holds true for $$0<a,b< \dfrac\pi2$$. Find the value of $$-\sin(a-b)$$.

×