# Trigonometric Identities - Help!!

Discussion in 'Mathematics' started by Bev179, Mar 28, 2011.

1. ### Bev179

I wonder if anybody could help explain please.

How to verify the trigonometric identity of this equation or if you could point me in the right direction of a good website

(cos? - cos³?) / (?(1-cos^2 ?)) = cos ec?

Thanks

Bev

2. ### shazgo

Is that (cos theta minus cos cubed theta) over the square root of (1 minus cos squared theta)? And should it equal cosec theta?

3. ### arsinhNew commenter

The two sides are not identical.

4. ### shazgo

So is it an equation to solve, rather than an identity to prove?

5. ### Bev179

Sorry. Son copied in two different questions Perhaps that is adding to his problems

Again

cos theta - cos cubed theta

over

Sin theta

equals

sin theta cos theta

6. ### arsinhNew commenter

Factorise the numerator.
Use sin&sup2;x = 1 - cos&sup2;x twice.

7. ### shazgo

In that case, factorise the numerator to give cos theta (1 minus cos squared theta) over sin theta. 1 minus cos squared theta is sin squared theta, so you have cos theta sin squared theta over sin theta and cancel one of the sin thetas.
Sorry that my lack of ICT skills means that I have to type out the words, but I hope this helps.
I have a whole book of these called "Trig or treat" but I don't think the author's idea of a treat matches that of the average sixth former!

8. ### shazgo

Cross posted with arsinh who was significantly more succinct than me!

9. ### Bev179

Thanks Shazgo and Arsinh, you've both been a big help.

I think he's got it.