MHB Minimum of $a$ for $a^2+2b^2+c^2+ab-bc-ac=1$

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Let $a,\,b,\,c$ be real numbers such that $a^2+2b^2+c^2+ab-bc-ac=1$. Find the minimum possible value of $a$.
 
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Hint:

Discriminant of quadratic equation helps...:)
 
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