[(sinx)^2-(cosx)^2]/[sinx^4+cosx^4]=-cos2x/[(sinx^2+cosx^2)^2-2sinx^2cosx^2]=-cos2x/1-(sin2x)^2/2∫[(sinx)^2-(cosx)^2]dx/[sinx^4+cosx^4]=∫-cos2xdx/[1-(sin2x)^2/2]=-∫dsin2x/(2-(sin2x)^2)=[-1/(2√2)]...