设I=∫(0,+∞)e^(-x^2)dx
4I^2=∫(-∞,+∞)∫(-∞,+∞)e^(-x^2-y^2)dxdy=∫(0,2π)dθ∫(0,+∞)re^(-r^2)dr
=2π×(1/2)=π
I=(√π)/2
求定积分e的负x平方的从0至正无穷积分
设I=∫(0,+∞)e^(-x^2)dx
4I^2=∫(-∞,+∞)∫(-∞,+∞)e^(-x^2-y^2)dxdy=∫(0,2π)dθ∫(0,+∞)re^(-r^2)dr
=2π×(1/2)=π
I=(√π)/2