Answer:
a^2 + b^2 - c^2 + 2ab
Step-by-step explanation:
(a + b - c)(a + b + c)
1. expand
(a^2 + ab + ac + ba + b^2 + bc - ca - cb - c^2)
2. rearrange,
(a^2 + b^2 - c^2 + ab + ba + ac - ca + bc - bc)
3. add and subtract
(a^2 + b^2 - c^2 + 2ab)
