题目内容
(1)化简:2a﹣5b+3a+b
(2)先化简,再求值:5(3a2b﹣ab2)﹣4(﹣3ab2+2a2b),其中a=﹣2,b=3
(3)化简:(x+y)2﹣(x﹣y)2+(x﹣y)2﹣(x+y)2﹣(x﹣y)2.
(2)先化简,再求值:5(3a2b﹣ab2)﹣4(﹣3ab2+2a2b),其中a=﹣2,b=3
(3)化简:(x+y)2﹣(x﹣y)2+(x﹣y)2﹣(x+y)2﹣(x﹣y)2.
解:(1)原式=5a﹣4b;
(2)原式=15a2b﹣5ab2+12ab2﹣8a2b=7a2b+7ab2,
当a=﹣2,b=3时,原式=7×(﹣2)2×3+7×(﹣2)×32=84﹣126=﹣42;
(3)原式=(x﹣y)2﹣2(x﹣y)2=﹣(x﹣y)2=﹣x2+2xy﹣y2.
(2)原式=15a2b﹣5ab2+12ab2﹣8a2b=7a2b+7ab2,
当a=﹣2,b=3时,原式=7×(﹣2)2×3+7×(﹣2)×32=84﹣126=﹣42;
(3)原式=(x﹣y)2﹣2(x﹣y)2=﹣(x﹣y)2=﹣x2+2xy﹣y2.
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