<s>[INST] 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.
 [/INST] $a^2 + b^2 +c^2 = \frac {a^2 + b^2}{2} + \frac {b^2 + c^2}{2} + \frac {a^2 + c^2}{2}= ab + bc + ac\\
\frac {a^2 -2ab +b^2}{2} + \frac {b^2 -2bc +c^2}{2} + \frac {a^2 -2ac +c^2}{2}= 0\\
(a-b)^2 + (b-c)^2 + (c-a)^2 = 0\\
a = b = c$
$\frac {a+b}{c} = 2$
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