先化简,再求值, (1)12(a2b-
(2)已知a-b=5,ab=-1,求(2a+3b-2ab)-(a+4b+ab)-(3ab+2b-2a)的值. |
(1)原式=12a2b-4ab2+5ab2-5a2b-2a2b-12
=5a2b+ab2-12,
当a=
,b=5时,原式=1+5-12=-6;1 5
(2)原式=2a+3b-2ab-a-4b-ab-3ab-2b+2a
=3a-3b-6ab
=3(a-b)-6ab,
当a-b=5,ab=-1时,原式=3×5-6×(-1)=15+6=21.
先化简,再求值, (1)12(a2b-
(2)已知a-b=5,ab=-1,求(2a+3b-2ab)-(a+4b+ab)-(3ab+2b-2a)的值. |
(1)原式=12a2b-4ab2+5ab2-5a2b-2a2b-12
=5a2b+ab2-12,
当a=
,b=5时,原式=1+5-12=-6;1 5
(2)原式=2a+3b-2ab-a-4b-ab-3ab-2b+2a
=3a-3b-6ab
=3(a-b)-6ab,
当a-b=5,ab=-1时,原式=3×5-6×(-1)=15+6=21.