Question

x－y＝6.y-z＝5求x²+y²+z²－xy-xz-yz的值

Answer 1

91！

1. (x-y)²=x²+y²-2xy;

2. (y-z)²=y²+z²-2zy;

3. (x-y)(y-z)=xy-xz-y²+yz;

    上面式子相加：

   (x-y)²+(y-z)²+(x-y)(y-z)=x²+y²-2xy+y²+z²-2zy+xy-xz-y²+yz；

                                         =x²+y²+z²－xy-xz-yz

Answer 2

追问

额，是y－z＝5.不是y-8=5

追答

Z呀

追问

o.不好意思，看错了

Answer 3