Question

(2x+y)2-(2x-y)(x+y)-2(x-2y)(x+2y),其中x= ,y=-2 化简求值

x+y+z=4,x²+y²+z²=2，求xy+yz+zx的值
要过程
两个问题

Answer 1

x²+y²+z²+2(xy+yz+zx)=(x+y+z)² = 4² = 16
x²+y²+z²=2

2(xy+yz+zx) = 16 - 2 = 14
xy+yz+zx = 7

Answer 2

7