y=1-tan^22x/1+tan^22x的最小周期

y=(1-sin²2x/cos²2x)/(1+sin²2x/cos²2x)
=(cos²2x-sin²2x)/(cos²2x+sin²2x)
=cos4x
T=2π/4=π/2
tan2x中2x≠kπ+π/2
x≠kπ/2+π/4
即不在y=±x上
即相邻两个角相差π/2,正号符合T=π/2
所以T=π/2