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nesmira · Sep 23, 2009, 04:29 PM

Prove the identity!

Cos (pi/2 - x) = sin X

Unknown008 · Sep 24, 2009, 07:45 AM

Use your formulae: $cos(A-B) = cosAcosB + sinAsinB$

$cos(\frac{\pi}{2} -x) = cos(\frac{\pi}{2})cos(x) + sin(\frac{\pi}{2})sin(x)$

$cos (\frac{\pi}{2}) = 0$

$sin(\frac{\pi}{2}) = 1$

$cos(\frac{\pi}{2})cos(x) + sin(\frac{\pi}{2})sin(x) = (0)cos(x) + (1)sin(x)$

That's all, it's almost finished. You only have to simplify.

I hope it helped! :)