For real $a,b,c$ , if $a^2+b^2+c^2=ab+bc+ac$ ,then the value of $\frac{a+b} {c}$ is? 
For real $a,b,c$ , if $a^2+b^2+c^2=ab+bc+ac$ ,then the value of
  $\frac{a+b} {c}$ is how much?

Ans.
What I could gather:
from the identity,
$$ a^3+b^3+c^3-3abc=(a+b+c)(a^2+b^2+c^3-ab+bc+ca)$$
We gather that RHS=0.
$$ =>a^3+b^3+c^3=3abc$$
It would e helpful if someone could tell me how should I proceed.

Another approach we can use is AM-GM inequality . 
$$\frac{a^2+b^2}{2} \ge \sqrt{a^2b^2}$$
$$\sum_{a,b,c}\frac{a^2+b^2}{2} \ge \sum{ab}$$
Now equality will hold only when $a=b=c$
