设X为随机变量，E(X)＝2，D(X)=4,则E( )=（ ）/ananas/latex/p/155342
设X为随机变量，E(X)＝2，D(X)=4,则E( )=（ ）/ananas/latex/p/155342
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设X为随机变量，E(X)＝2，D(X)=4,则E( )=（ ）/ananas/latex/p/155342