数学定积分

另X=sint，则-π/2≤t≤π/2，dx=costdt

原式=∫cost*costdt（下限-π/2，上限π/2）=∫（cos2t+1）/2dt（下限-π/2，上限π/2）=

[1/4*sin2t+t/2](下限-π/2，上限π/2）=（1/4sinπ+π/4）-（1/4sin-π+（/π/4））=π/2