# Prove the identity

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• Aug 3rd 2009, 11:10 AM
Yuroichi
Prove the identity
$4sin2xcos2x=2sin4x$

$6cot^22x-csc^22x=6cos^32x$
• Aug 3rd 2009, 11:46 AM
e^(i*pi)
Quote:

Originally Posted by Yuroichi
$4sin2xcos2x=2sin4x$

$6cot^22x-csc^22x=6cos^32x$

1. Use the double angle identity $sin(2u) = 2sin(u)cos(u)$.
In this case $u=2x$

2. This is not an identity - try $x = 1.25\pi$

$\frac{6cos^2(2x)-1}{sin^2(2x)}$