Question

If a,b,c are in A.P. then:
(a-b)^2+(a-c)^2+(b-c)^2=6(b^2-ac)?


I know that (a-c)^2=4(b2-ac), but I don't know what to do with (a-b)^2 and (b-c)^2

Help please
Thanks in advance

Answer 1

Please see the attachment