由于tanu/sec^2(u)是奇函数，所以∫(-π/4→π/4)tanu/sec^2(u)du=0由于1/sec^2(u)=cos^2(u)是偶函数，所以∫(-π/4→π/4)cos^2(u)du=2∫(0→π/4)cos^2(u)du
因为是奇函数嘛 所以为0咯
