题目运用留数定理计算积分 int_(0)^infty (1)/(x^2+1) dx = ( )A. piB. pi/2C. 2piD. 0运用留数定理计算积分 $\int_{0}^{\infty} \frac{1}{x^2+1} dx =$ ( )A. $\pi$B. $\pi/2$C. $2\pi$D. $0$题目解答答案B. $\pi/2$