[(3m+2n)+(3m+2n+m-n)]*2
=(7m+3n)*2
=14m+6n已知关于x、y的多项式2mx^3+3nxy^2-2x^3-xy^2-2x+y中不含三次项,求2m+3n的值。因为不含三次项，所以2m-2=0m=12m+3n=2*1+3n=3n+2