how do i simplify this:
(sin^2(a)+2cos(a)-1)
and make it into
(2cos(a)-cos^2(a))
Surely if $\displaystyle \displaystyle \begin{align*} \sin^2{\theta} + \cos^2{\theta} \equiv 1 \end{align*} $ then $\displaystyle \displaystyle \begin{align*} \sin^2{\theta} \equiv 1 - \cos^2{\theta} \end{align*} $
Substitute this in place of $\displaystyle \displaystyle \begin{align*} \sin^2{\theta} \end{align*} $.
You've asked very similar questions in about four different threads, surely you have learnt something by now...