Let $a,$ $b,$ and $c$ be real numbers such that $a^2 + b^2 + c^2 = 1.$  Find the minimum value of
\[ab + ac + bc.\]
Question:
Let $a,$ $b,$ and $c$ be real numbers such that $a^2 + b^2 + c^2 = 1.$  Find the minimum value of
\[ab + ac + bc.\]
Answer:
Let's think step by step.

user
-\frac{1}{2}
Let $a,$ $b,$ and $c$ be real numbers such that $a^2 + b^2 + c^2 = 1.$  Find the minimum value of
\[ab + ac + bc.\]
train