Can someone help explain this trigonometry equation to me with a detailed development?

sin^{2}a - cos^{2}a = 1-2 x cos^{2}a

thank you!

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- Oct 23rd 2013, 11:10 AMnova23help with trigonometry
Can someone help explain this trigonometry equation to me with a detailed development?

sin^{2}a - cos^{2}a = 1-2 x cos^{2}a

thank you! - Oct 23rd 2013, 12:35 PMebainesRe: help with trigonometry
One of the most basic identities to memorize because you will use it frequently is: $\displaystyle \sin^2a + \cos^2a = 1$. Rearrange this to get the $\displaystyle \sin^2a$ by itself, and then substitute for the $\displaystyle \sin^2a$ term in your equation - what do you get? By the way, you could also have replaced the $\displaystyle \cos^2a$ term in your equation to get a different form of the same equation, all of which are equal to $\displaystyle \cos(2a)$.

- Oct 23rd 2013, 01:52 PMnova23Re: help with trigonometry
thank you.

but can you or someone else explain even clearer how to develop and explain the equation, i'm new to maths and trigonometry and really need a full explanation as detailed as possible! - Oct 23rd 2013, 02:12 PMPlatoRe: help with trigonometry