证明：左边=1+sinα/1-sinα
右边=(1/cosα+tanα)^2
=(1/cosα+sinα/cosα)^2
=(1+sinα/cosα) ^2
=(1+sinα) ^2/(cosα)^2
=(1+sinα) ^2/1-(sinα)^2
=(1+sinα) ^2/(1+sinα)(1-sinα)
=1+sinα/1-sinα
=左边
即证.