设随机变量X~N(0,1),N(0,1)且X,Y相互独立 求 E[X^2/(X^2+Y^2)]因为X,Y相互独立,所以E[X^2/(X^2+Y^2)]=E[Y^2/(X^2+Y^2)].而E[X^2/(X^2+Y^2)]+E[Y^2/(X^2+Y^2)]=E[(X^2+Y^2)/(X^2+Y^2)]=1.所以E[X^2/(X^2+Y^2)]=1/2.为什么E[(X^2+Y^2)/(X^2+Y^2)
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![设随机变量X~N(0,1),N(0,1)且X,Y相互独立 求 E[X^2/(X^2+Y^2)]因为X,Y相互独立,所以E[X^2/(X^2+Y^2)]=E[Y^2/(X^2+Y^2)].而E[X^2/(X^2+Y^2)]+E[Y^2/(X^2+Y^2)]=E[(X^2+Y^2)/(X^2+Y^2)]=1.所以E[X^2/(X^2+Y^2)]=1/2.为什么E[(X^2+Y^2)/(X^2+Y^2)](/uploads/image/z/6603325-61-5.jpg?t=%E8%AE%BE%E9%9A%8F%E6%9C%BA%E5%8F%98%E9%87%8FX%7EN%280%2C1%29%2CN%280%2C1%29%E4%B8%94X%2CY%E7%9B%B8%E4%BA%92%E7%8B%AC%E7%AB%8B+%E6%B1%82+E%5BX%5E2%2F%28X%5E2%2BY%5E2%29%5D%E5%9B%A0%E4%B8%BAX%2CY%E7%9B%B8%E4%BA%92%E7%8B%AC%E7%AB%8B%2C%E6%89%80%E4%BB%A5E%5BX%5E2%2F%28X%5E2%2BY%5E2%29%5D%3DE%5BY%5E2%2F%28X%5E2%2BY%5E2%29%5D.%E8%80%8CE%5BX%5E2%2F%28X%5E2%2BY%5E2%29%5D%2BE%5BY%5E2%2F%28X%5E2%2BY%5E2%29%5D%3DE%5B%28X%5E2%2BY%5E2%29%2F%28X%5E2%2BY%5E2%29%5D%3D1.%E6%89%80%E4%BB%A5E%5BX%5E2%2F%28X%5E2%2BY%5E2%29%5D%3D1%2F2.%E4%B8%BA%E4%BB%80%E4%B9%88E%5B%28X%5E2%2BY%5E2%29%2F%28X%5E2%2BY%5E2%29)
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