作者PrinceAries (This is Aries Speaking)
站内Statistics
标题[问题] 条件机率的证明
时间Wed Mar 11 16:21:46 2009
这是原题目：
Let X and Y are two independent discrete random variables.
Prove that the following equation of the conditional probability:
P(X=x) = ΣP(X=x│Y=y)．P(Y=y)
y (Σ从y开始加)
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一般来说，
P (x│y) = P (x,y) / P (y)
X│Y XY Y
P (x,y) = P (x│y)．P (y)
XY X│Y Y
ΣP (x,y) = ΣP (x│y)．P (y)
y XY y X│Y Y
P (x) = ΣP (x│y)．P (y)
X y X│Y Y
这样有得证吗?
是写法不同还是从题目倒推?
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