设f(x,y)为连续函数,交换二次积分I=∫(0,1)x^2dx∫(x,1)(e^(-y^2))dy的积分次序后则I=

Question

设f(x,y)为连续函数,交换二次积分I=∫(0,1)x^2dx∫(x,1)(e^(-y^2))dy的积分次序后则I=

Answer 1

I=∫(0,1)x^2dx∫(x,1)(e^(-y^2))dy
=∫(0,1)e^(-y^2)dy∫(0,y)x^2dx
=1/3∫(0,1)y^3*e^(-y^2)dy
=-1/6∫(0,1)y^2*d(e^(-y^2))
=-1/6y^2*e^(-y^2)[0,1]+1/3∫(0,1)y*e^(-y^2)dy
=-1/(6e)-1/6e^(-y^2)[0,1]
=-1/(6e)-1/(6e)+1/6
=1/6-1/(3e)