Prove that `a^2+b^2+c^2-a b-b c-c a` is always non-negative for all values of `a ,b and `c` cdot`

Explanation

To prove that the expression \( a^2 + b^2 + c^2 - ab - ac - bc \) is always non-negative for all values of \( a, b, \) and \( c \), we can follow these steps:

### Step 1: Rewrite the Expression
We start with the expression:
\[ E = a^2 + b^2 + c^2 - ab - ac - bc \]

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