Question

已知A＝3a²-3ab+b²，B＝3a²-2ab，C＝a²-ab，试计算A-2B+3C

Answer 1

已知A=3a的平方-3ab+b的平方,B=3a的平方-2ab,C=a的平方-ab,试着计算A-2B+.C=a的平方-ab，试着计算A-2B+3C
A-2B+.C=3a^2-3ab+b^2-2(3a^2-2ab)+a^2-ab=3a^2-3ab+b^2-6a^2+4ab+a^2-ab=-2a^2+b^2
A-2B+3C=3a^2-3ab+b^2-2(3a^2-2ab)+3(a^2-ab)=3a^2-3ab+b^2-6a^2+4ab+3a^2-3ab=b^2-2ab

Answer 2

A-2B+3C
=3a²-3ab+b²-2(3a²-2ab)+3(a²-ab)
=3a^2-3ab+b^2-6a^2+4ab+3a^2-3ab
=(3-6+3)a^2+(-3+4-3)ab+b^2
=b^2-2ab