x²-y²=1
1/x²+2y/x
设 x=secm,
则 y=tanm
1/x²+2y/x
=cos^m+2tanm*cosm
=cos^m+2sinm
=1-sin^m+2sinm
=2-(sinm-1)^2
所以
-2谢谢，知道了。那请问cos²36°+cos²72°=？谢谢、cos²36°+cos²72°=cos²36°+1/2（2sin^18°-1+1）=cos²36°+1/2（-cos36°+1）=cos²36°-1/2cos36°+1/2答案是3/4原式=1-sin²36+sin²18=1+(sin18+sin36)(sin18-sin36)=1+[sin(27-9)+sin(27+9)][sin(27-9)-sin(27+9)]=1+(sin27cos9-cos27sin9+sin27cos9+cos27sin9)(sin27cos9-cos27sin9-sin27cos9-cos27sin9)=1-4sin27cos9cos27sin9=1-(2sin27cos27)(2sin9cos9)=1-sin18sin54=1-2sin18cos18cos36/2cos18=1-sin36cos36/2cos18=1-sin72/4sin72=1-1/4=3/4