(1)x^2+7x-18(2)y^2+7y+10(3)x^2-2x-8(4)(a+b+c)^2-(a-b-c)^2(5)已知x^2+y^2+2x-6y+10=0,求x+y的值（注意标清序号..）

Question

(1) x^2+7x-18
(2) y^2+7y+10
(3) x^2-2x-8
(4) (a+b+c)^2-(a-b-c)^2
(5) 已知x^2+y^2+2x-6y+10=0,求x+y的值
（注意标清序号..）

Answer 1

(1) x^2+7x-18
=(x-2)(x+9)
(2) y^2+7y+10
=(x+2)(x+5)
(3) x^2-2x-8
=(x+2)(x-4)
(4) (a+b+c)^2-(a-b-c)^2
=(a+b+c+a-b-c)(a+b+c-a+b+c)
=2a(2b+2c)
=4a(b+c)
(5) 已知x^2+y^2+2x-6y+10=0,求x+y的值
(x+1)²+(y-3)²=0
x+1=0,y-3=0
x=-1,y=3
x+y=-1+3=2