(1+Sin4x+Cos4x)/(1+Sin4x-Cos4x)
=[1+Sin4x+2(Cos2x)^2-1]/{1+Sin4x-[1-2(Sin2x)^2]}
=[Sin4x+2(Cos2x)^2]/[Sin4x+2(Sin2x)^2]
=[2Sin2xCos2x+2(Cos2x)^2]/[2Sin2xCos2x+2(Sin2x)^2]
=Cos2x/Sin2x
=Cot2x
所以
原式=1/Cot2x - Cot2x