原式=∫dz∫dy∫xdx=∫dz∫(1/2)(1-y-z)^2dy=(1/2)∫dz∫[(1-z)^2-2(1-z)y+y^2]dy=(1/6)∫(1-z)^3*dz=(1/6)∫(1-3z+3z^2-z^3)dz=(1/6)(z-3z^2/2+z^3-z^4/4)|=(1/6)(1-3/2+1-1/4)=1/24.