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.
答
∵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.