解1：3(-ab+2a)-(3a-b)+3ab
=3×(-ab)+3×2a-3a+b+3ab
=-3ab+6a-3a+b+3ab
=(-3ab+3ab)+(6a-3a)+b
=3a+b
解2：2a²-[0.5(ab-a²)+8ab]-0.5ab
=2a²-(0.5ab-0.5a²+8ab)-0.5ab
=2a²-0.5ab+0.5a²-8ab-0.5ab
=(2a²+0.5a²)+(-0.5ab-8ab-0.5ab)
=2.5a²-9ab
解3：7x²-5x+3-2x+3x²-5
=(7x²+3x²)+(-5x-2x)+(3-5)
=10x²-7x-2
解4：-2(xy-3y²)-[2y²-5(xy+x²)+2xy]
=-2xy+6y²-(2y²-5xy-5x²+2xy)
=-2xy+6y²-2y²+5xy+5x²-2xy
=5x²+(6y²-2y²)+(-2xy+5xy-2xy)
=5x²+4y²+xy
解二
(1)原式=(4a+3a²-3+3a³)-(-a+4a³)
=4a+3a²-3+3a³+a-4a³
=(3a³-4a³)+3a²+(4a+a)-3
=-a³+3a²+5a-3
当a=-2时
原式=-(-2)³+3×(-2)²+5×(-2)-3
=-(-8)+3×4-10-3
=8+12-13
=7
(2)原式=(2x²y-2xy²)-[(-3x²y²+3x²y)+(3x²y²-3xy²)]
=2x²y-2xy²-(-3x²y²+3x²y+3x²y²-3xy²)
=2x²y-2xy²+3x²y²-3x²y-3x²y²+3xy²
=(2x²y-3x²y)+(-2xy²+3xy²)+(3x²y²-3x²y²)
=-x²y+xy²
=xy²-x²y
当x=-1,y=2时
原式=(-1)×2²-(-1)²×2
=(-1)×4-1×2
=-4-2
= -6
