丨x-8y丨+2(4y-1)²+丨8z-3x丨=0
所以x-8y=0 4y-1=0 8z-3x=0
解得：x=2 y=1/4 z=3/4
x+4y+12z
=2+4×1/4+12×3/4
=2+1+9
=12