We are asked to expand the expression $(a-b-c)^2$.

1. Problem Description

We are asked to expand the expression $(a-b-c)^2$.

2. Solution Steps

We can rewrite the expression as follows:

$(a - b - c)^2 = (a - (b+c))^2$

We can use the formula for the square of a difference:

$(x - y)^2 = x^2 - 2xy + y^2$

In our case, $x = a$ and $y = b+c$.

So,

$(a - (b+c))^2 = a^2 - 2a(b+c) + (b+c)^2$

Now, we need to expand $(b+c)^2$:

$(b+c)^2 = b^2 + 2bc + c^2$

Substitute this back into the expression:

$a^2 - 2a(b+c) + (b+c)^2 = a^2 - 2ab - 2ac + b^2 + 2bc + c^2$

Rearranging the terms, we get:

$a^2 + b^2 + c^2 - 2ab - 2ac + 2bc$

3. Final Answer

$a^2 + b^2 + c^2 - 2ab - 2ac + 2bc$