(sin^4(x) + cos^4(x) +2sin^2(x) cos^2(x) ) -2sin^2(x) cos^2(x) = 7/8
(sin ^2(x) + cos^2(x))^2 - 2sin^2(x) cos^2(x) = 7/8
1-2sin^2(x) cos^2(x) = 7/8
2sin^2(x) cos^2(x) = 1/8
sin^2(x) cos^2(x) = 1/16
2cos(4x)= 1
cos (4x) = 1/2
4x = +_ pi/3+2pin
x = +_ pi/12 + pin/2