(x-4)^2+1/4|x+y-z|=0因为(x-4)^2+1/4|x+y-z|=0所以x-4=0 x+y-z=0x=4 y-z=-4将x=4 y-z=-4代入（5x+3y-3z）=5*4+3*(-4)=20-12=8
