2x(1/2x²-1）-3x(1/3x²+2/3）
=x³-2x-x³-2x
=-4x;
[x(x²y²-xy)-y(x²-x³y)]÷3x²y
=(x³y²-x²y-x²y+x³y²)÷3x²y
=2xy/3-2/3;
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