题目内容：

设（ζ,η）服从在A上的均匀分布,其中A为x轴、y轴及直线x+y+1=0所围成的区域,求E（ζη）

优质解答

1/12f(x,y)=2 in A,=0,otherwise.E{XY}= (x from -1 to 0)(y from y=-1-x to 0)∫∫2xydxdy=2(x from -1 to 0)∫x[(y from y=-1-x to 0)∫ydy]dx=-(x from -1 to 0)∫x(1+x)²dx=-(x from -1 to 0)∫(x³+2x...