Let f(x,y)=6(1−x−y)f(x, y) = 6(1-x-y)f(x,y)=6(1−x−y) for x,y≥0x, y \ge 0x,y≥0 and x+y≤1x+y \le 1x+y≤1. What is the marginal PDF fX(x)f_X(x)fX(x)?
3(1−x)23(1-x)^23(1−x)2
6(1−x)6(1-x)6(1−x)
1−x1-x1−x
3(1−x)3(1-x)3(1−x)