计算下列定积分: ∫π/20cosx/(1+sin2x)dx

计算下列定积分:
π/20cosx/(1+sin2x)dx
【正确答案】:∫π/20cosc/(1+sin2)dx =∫π/201/(1+sin2)d(sinx) =arctan(sinx)|π/20 =π/4