已知xyz=1,x+y+z=2,x方+y方+z方=16,求xy+1/2z+yz+1/2x+zx+1/2y=?
问题描述:
已知xyz=1,x+y+z=2,x方+y方+z方=16,求xy+1/2z+yz+1/2x+zx+1/2y=?
答
x+y+z=2 那么(x+y+z)方=4=x方+y方+z方+2xy+2xz+2yz,xy+1/2z+yz+1/2x+xz+1/2y=xy+yz+zx+1/2(x+y+z),4=16+2(xy+xz+yz) 综上所述答案为-5