(1)原式=2a2b+2b2a-[2a2b-2+3ab2+2]
=2a2b+2b2a-2a2b+2-3ab2-2
=-ab2
当a=2,b=-2时,原式=-2×(-2)2=-8.
(2)由题意知,A=(7a2-7ab)+2B
=(7a2-7ab)+2(-4a2+6ab+7)
=7a2-7ab-8a2+12ab+14
=-a2+5ab+14
∵|a+1|+(b-2)2=0,
∴a+1=0,b-2=0,即a=-1,b=2.
当a=-1,b=2时,原式=-1-10+14=3.
(3)(2mx2-x2+3x+1)-(5x2-4y2+3x)
=2mx2-x2+3x+1-5x2+4y2-3x
=(2m-6)x2+4y2+1
∵不含x2项
∴2m-6=0,解得m=3.
∴2m3-[3m3-(4m-5)+m]
=2m3-[3m3-4m+5+m]
=2m3-3m3+4m-5-m
=-m3+3m-5
当m=3时
原式=-27+9-5=-23.