SOLUTION: Prove that {{{ Cos^4A - Sin^4A = 1

SOLUTION: Prove that {{{ Cos^4A - Sin^4A = 1 - 2Sin^2A }}}

Question 495314: Prove that

Answer by lwsshak3(11628) (Show Source): You can put this solution on YOUR website!
Prove:
Cos^4A - Sin^4A = 1 - 2Sin^2A
Starting with left side
cos^4-sin^4
=(cos^2+sin^2)(cos^2-sin^2)
=(cos^2+sin^2)(1-sin^2-sin^2)
=1(1-2sin^2)
=1-2sin^2
verified:
left side = right side
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