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.

Hint:
$$a^2+b^2+c^2=ab+bc+ca \Leftrightarrow $$
$$\Leftrightarrow 2a^2+2b^2+2c^2=2ab+2bc+2ca \Leftrightarrow$$
$$\Leftrightarrow a^2-2ab+b^2+b^2-2bc+c^2+c^2-2ca+a^2=0 \Leftrightarrow$$
$$\Leftrightarrow (a-b)^2+(b-c)^2+(c-a)^2=0 \Leftrightarrow a=b=c$$
