已知A=a2-2ab+b2,B=-a2-3ab-b2,求:2A-3B.

问题描述:

已知A=a2-2ab+b2,B=-a2-3ab-b2,求:2A-3B.

∵A=a2-2ab+b2,B=-a2-3ab-b2
∴2A-3B,
=2(a2-2ab+b2)-3(-a2-3ab-b2
=2a2-4ab+2b2+3a2+9ab+3b2
=5a2+5ab+5b2