# Yet another Trig identity

• August 14th 2009, 03:50 PM
GeoffP
Yet another Trig identity
Removed
• August 14th 2009, 04:15 PM
Chris L T521
Quote:

Originally Posted by GeoffP
Q. Prove Cot^2t-Cos^2t=Cot^2t . Cos^2t

I have changed to sines/Cosines but seem to end up going round in circles. I have also tried working on both sides.

I think i need a combination of Cos^2t= 1- Sin^2t and Cot^2t = Cos^2t / Sin^2 t.

Any assistance appreciated.

Cheers

Note that $\cot^2t-\cos^2t=\frac{\cos^2t}{\sin^2t}-\cos^2t=\left(\frac{1}{\sin^2t}-1\right)\cos^2t=\left(\csc^2t-1\right)\cos^2t$

Apply another identity, and you're done.