§（e^-x^2）xdx
=-1/2∫e^(-x^2)d(-x^2)
=-1/2e^(-x^2)+c
§a^xdx/(a^2x+1)
=1/lna§1/(a^2x+1)d(a^x)
=1/lna*arctan(a^x)+c
用凑微分法求§（e^-x^2）xdx、§a^xdx/(a^2x+1)、的不定积分
§（e^-x^2）xdx
=-1/2∫e^(-x^2)d(-x^2)
=-1/2e^(-x^2)+c
§a^xdx/(a^2x+1)
=1/lna§1/(a^2x+1)d(a^x)
=1/lna*arctan(a^x)+c