|X-3|与(x+y+4)²互为相反数,那么|x-3|+(x+y+4)²=0
所以,x-3=0,x+y+4=0
所以,x=3,y=-7
(3x-y+1) - 3(x+y+1/2)
=(9+7+1) - 3(3-7+1/2)
=17 + 21/2
=55/2