FZ ( z )
x y z
f ( x, y)dxdy z y
化成累次积分,得
FZ ( z ) [
f ( x, y)dx ]dy
变量代换 固定z和y,对方括号内的积分作变量代换, 令x=u-y,得
FZ ( z ) [ f ( u
y, y)du]dy z
z
交换积分次序
[ f ( u y, y)dy]du
FZ ( z )
x y z
f ( x, y)dxdy z y
化成累次积分,得
FZ ( z ) [
f ( x, y)dx ]dy
变量代换 固定z和y,对方括号内的积分作变量代换, 令x=u-y,得
FZ ( z ) [ f ( u
y, y)du]dy z
z
交换积分次序
[ f ( u y, y)dy]du
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