cos2x+sinx四次方=1-2(sinx)^2+(sinx)^4=(1-(sinx)^2)^2=(sinx)^4
cosx四次方-cos2x=(1-(cosx)^2)^2=(cosx)^4
根号（cos2x+sinx四次方）+根号（cosx四次方-cos2x）=(sinx)^2+(cosx)^2=1