Question 495314
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