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4443223: ½ð±Ò+5, ¡ï¡ï¡ï¡ï¡ï×î¼Ñ´ð°¸, º¾ÎÒÃÇ×öÅóÓÑ°É 2013-12-24 08:46:09
feixiaolin: ½ð±Ò+1, zan 2013-12-24 11:01:30
ÒòΪ XµÄ¾ùֵΪN£¬·½²îΪD£¬
ËùÒÔÓÐ E(X^2)= D(X) +[E(X)]^2= D +N^2

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Ôò E(Y^3) = 0
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X = Y * D^0.5 +N
X^3 = [(Y*D^0.5) + N]^3 = Y^3 * D^1.5 + 3* Y^2 *D*N + 3*Y*N^2*D^0.5 + N^3
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E(X^3) = 3 *D*N E(Y^2) + N^3 = 3 DN  + N^3
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