Question

2(sin^4 x + cos^4 x) =1 [ - pi ≤ x ≤ pi ]

Answer 1

(sin^2 x +cos^2 x)^2 -2(sinxcosx)^2=1/2

1-2(sinxcosx)^2=1

sin2x=...

又x∈[-pi,pi]

所以x=...