sin^4x+cos^4x-3/4 =sin^4x+2sin^2xcos^2x+cos^4x-2sin^2xcos^2x-3/4 =(sin^2x+cos^2)^2-2sin^2xcos^2x-3/4 =1-2sin^2xcos^2x-3/4 =1/4-2sin^2xcos^2x=1/4-1/2(sin2x)^2=1/4-1/2(sin2x)^2=1/4-1/2[(1-cos4x)/2]=1/4-...