∫(0~无穷)∫(0~1)(x+y)(e^-y)dxdy
=∫(0~无穷){(x²/2+xy)(e^-y) ](x:0~1) }dy
=∫(0~无穷){(1/2+y)(e^-y) }dy
=∫(0~无穷){y(e^-y) }dy+∫(0~无穷)1/2(e^-y) ]dy
=gamma(2)+1/2gamma(1)
=1+1/2
=3/2
∫(0~无穷)∫(0~1)(x+y)(e^-y)dxdy
=∫(0~无穷){(x²/2+xy)(e^-y) ](x:0~1) }dy
=∫(0~无穷){(1/2+y)(e^-y) }dy
=∫(0~无穷){y(e^-y) }dy+∫(0~无穷)1/2(e^-y) ]dy
=gamma(2)+1/2gamma(1)
=1+1/2
=3/2