先化简,再求值. (1)[(x+y)2-y(2x+y)-8x]÷2x,其中x=-2. (2)(x+3y)2+(2x+y)(x-y)

问题描述:

先化简,再求值.
(1)[(x+y)2-y(2x+y)-8x]÷2x,其中x=-2.
(2)(x+3y)2+(2x+y)(x-y)

(1)原式=(x2+2xy+y2-2xy-y2-8x)÷2x=(x2-8x)÷2x=

1
2
x-4,
当x=-2时,原式=
1
2
×(-2)-4=-5;
(2)原式=x2+6xy+9y2+2x2-xy-y2=3x2+5xy+8y2