Question

已知A-B=2,B-C=3,则求A的平方加B的平方加C的平方减AB的积减BC的积减AC的积的值?~~~~!

初2拓展题,高手解~!!~~~?

Answer 1

A-B=2,B-C=3 两式相加则A-C=5
原式=1/2 ((A-B)^2+(B-C)^2+(A-C)^2)
=19

Answer 2

a²+b²+c²-ab-bc-ac
=[(a-b)²+(b-c)²+(c-a)²]/2
=4+9+25=38