prove that 1+cos^2x =2(cos^4x+sin^4x)
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RHS
2(cis^4x + sin^4x)
2{(cos^2x+sin^2x)^2-2sin^2(2x)}
2{1-2sin^2(2x)}
LHS
1+cos^2(2x)
2(1-2sin^2(2x))
so LHS=RHS
prove
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Solutions:
x = π n, n element Z
x = π n - (2 π)/3, n element Z
x = π n - (4 π)/3, n element Z
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