A+2B=(6m的平方-10m+14,)+2(3m的平方+4m-11)
=6m²-10m+14+6m²+8m-22
=12m²-2m-8
2A-B=2(6m的平方-10m+14)-(3m的平方+4m-11)
=12m²-20m+28-3m²-4m+11
=9m²-24m+39