(∫∞,-∞ exp(-x^2) dx)*(∫∞,-∞ exp(-x^2) dx)=(∫∞,-∞exp(-x^2) dx)*(∫∞,-∞ exp(-y^2) dy)将上式化成在极坐标下的积分,原式=∫∫∞,-∞exp(-x^2-y^2) dxdy=∫2π,0 dt∫∞,0 exp(-r^2)rdr=2π*1/2...