化简
(1)
(2)2a﹣(5a﹣3b)+(7a﹣b)
(3)化简求值:2x 2+(﹣x 2﹣2xy+2y 2)﹣2(x 2﹣xy+2y 2),其中x=3,y=﹣2.
(1)
=2xy+2xy﹣
+
=4xy+
;
(2)2a﹣(5a﹣3b)+(7a﹣b)
=2a﹣5a+3b+7a﹣b
=4a+2b;
(3)2x 2+(﹣x 2﹣2xy+2y 2)﹣2(x 2﹣xy+2y 2)
=2x 2﹣x 2﹣2xy+2y 2﹣2x 2+2xy﹣4y 2
=﹣x 2﹣2y 2,
当x=3,y=﹣2时,﹣x 2﹣2y 2=﹣3 2﹣2×(﹣2) 2=﹣17.