问题
解答题
先化简后求值:
(1)2(a2b+ab2)-(a2b-1)-2ab2,其中,a=-1,b=2
(2)已知x-3y=6,xy=3,求代数式-2x+2[6y-(x-3xy)]-3xy的值.
答案
(1)2(a2b+ab2)-(a2b-1)-2ab2
=2a2b+2ab2-a2b+1-2ab2
=a2b+1,
当a=-1,b=2时,原式=(-1)2×2+1=3;
(2)-2x+2[6y-(x-3xy)]-3xy
=-2x+12y-2x+6xy-3xy
=-4x+12y+3xy
=-4(x-3y)+3xy,
当x-3y=6,xy=3,原式=-4×6+3×3=-15.