1 9x-6y-5x+4y
=4x-2y
2 3-1+x+1-x+x²
=3+x²
3 2x²-2y²+2-2x²-2y²+xy
=2+xy
4 3x-2y+4x(z+3y)
=3x-2y+4xz+12xy
5 15a²b-5ab²+12ab²-12a²b
=3a²b+7ab²
=ab(3a+7b)
将a=-2 b=3代入
=-6（3x-2+21)
=-6x15
=-90
6 3a+2b-3a(4a-3b)
=3a+2b-12a²+9ab
将a=-1 b=3代入
=3x-1+6-12+(-9)x3
=-3+6-12-27
=3-12-27
=-9-27
=-36
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