If cosA is not equal to 1, then sin^2A/(1-cosA) =

A) 1 + cosA
B) cosA
C) 1-cosA
D) 1
E) cosA -1

Remember the mother of all trig identities:

\sin^2 A + \cos^2 A = 1

The minute you see that \sin^2 A in there you should be thinking of that identity. Rearrange it so that you can do some substituting:

\sin^2 A =1- \cos^2 A

Now here’s what you’re working with:

\dfrac{1- \cos^2 A}{1- \cos A}

Now let’s get nuts and factor the difference of two squares up there in the numerator:

\dfrac{(1+ \cos A)(1- \cos A)}{1- \cos A}

Of course, you can simplify that to just 1+\cos A

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