用二维概率密度公式来求
Fz(z)=∫∫[x+yz-y] 1/2 dxdy=z/2-1/4
z∈[2,3]时,Fz(z)=∫∫[x+y1]∫[0->z-y] 1/2 dxdy - ∫[2->z]∫[0->z-x] 1/2 dydx=3z/2-(z^2)/4-5/4
0,z3
故f(x)= z/2,z∈[0,1]
1/2,z∈[1,2]
3/2-z/2,z∈[2,3]