設(shè)隨機(jī)變量X服從參數(shù)為2的泊松分布，則D(9—2X)=（ ）。???????
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常見隨機(jī)變量的方差
???????若X服從泊松分布，則D（X）=2，D(9—2X)=4D（X）=8。???????
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