把下列各式分解因式: (1)1/2a2+ab+1/2b2; (2)(x-y)(x-3y)+y2.

问题描述:

把下列各式分解因式:
(1)

1
2
a2+ab+
1
2
b2;                         
(2)(x-y)(x-3y)+y2

(1)原式=

1
2
(a2+2ab+b2
=
1
2
(a+b)2
(2)原式=x2-3xy-xy+3y2+y2=x2-4xy+4y2
=(x-2y)2