需要详解。
tan^2a +1=2（卜者链嫌谈tan^2b+1) 所以型孙1/cos^2a=2/ cos^2b
2cos^2a=cos^2b=1-sin^2b
1+cos2a=1-sin^2b cos2a +sin^2b=0
sin^2a/咐销cos^2a=(2sin^2b+cos^2b)/橘简耐cos^2b=(1+sin^2b)/圆春cos^2b
sin^2acos^2b=cos^2a+cos^2asin^2b
=(1-cos^2a)(1-sin^2b)
=1-cos^2a-sin^2b+sin^2bcos^2a
1=2cos^2a+sin^2b
=1+cos2a+sin^2b
cos2a+sin^2b=0