∫2x^e/(e^2x+9)dx
问题描述：
∫2x^e/(e^2x+9)dx
不好意思弄错了。正确的是：∫2e^x/(e^2x+9)dx
答
令t=e^x,则原式化为:
2∫ dt/(t^2+9) = (2/3)∫ d(t/3)/(1+(t/3)^2) = (2/3)arctan(t/3) = (2/3) arctan(e^x / 3)