边缘概率密度到底怎么求啊?f(x,y)=(6/((x+y+1)的四次方)x>0 y>0 其他都为0fY(y)=(6/((x+y+1)的四次方))dx 正无限到0的积分等于2/((y+1)的三次方),我理解不了这个为什么X会消失的?
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![边缘概率密度到底怎么求啊?f(x,y)=(6/((x+y+1)的四次方)x>0 y>0 其他都为0fY(y)=(6/((x+y+1)的四次方))dx 正无限到0的积分等于2/((y+1)的三次方),我理解不了这个为什么X会消失的?](/uploads/image/z/3839916-12-6.jpg?t=%E8%BE%B9%E7%BC%98%E6%A6%82%E7%8E%87%E5%AF%86%E5%BA%A6%E5%88%B0%E5%BA%95%E6%80%8E%E4%B9%88%E6%B1%82%E5%95%8A%3Ff%28x%2Cy%29%3D%286%2F%EF%BC%88%28x%2By%2B1%29%E7%9A%84%E5%9B%9B%E6%AC%A1%E6%96%B9%EF%BC%89x%3E0+y%3E0+%E5%85%B6%E4%BB%96%E9%83%BD%E4%B8%BA0fY%28y%29%3D%EF%BC%886%2F%28%28x%2By%2B1%29%E7%9A%84%E5%9B%9B%E6%AC%A1%E6%96%B9%29%EF%BC%89dx+%E6%AD%A3%E6%97%A0%E9%99%90%E5%88%B00%E7%9A%84%E7%A7%AF%E5%88%86%E7%AD%89%E4%BA%8E2%2F%EF%BC%88%28y%2B1%29%E7%9A%84%E4%B8%89%E6%AC%A1%E6%96%B9%EF%BC%89%2C%E6%88%91%E7%90%86%E8%A7%A3%E4%B8%8D%E4%BA%86%E8%BF%99%E4%B8%AA%E4%B8%BA%E4%BB%80%E4%B9%88X%E4%BC%9A%E6%B6%88%E5%A4%B1%E7%9A%84%3F)
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