积分下限负无穷,上限正无穷 dx/(1＋x^2)=
问题描述：
积分下限负无穷,上限正无穷 dx/(1＋x^2)=
答
∫(-∞,+∞)dx/(1＋x^2)
=2∫(0,+∞)dx/(1＋x^2)
=2arctanx ( 0,+∞)
=2[(π/2)-0]
=π