2a^2 + 2ac - 2ab - 2ab + 2b^2 + 2bc + 2ac - 2bc =2a^2 + 2b^2 - 4ab + 2ac + 2ac =2(a^2 + b^2 - 2ab + ac)
2a^2 + 2ac - 2ab - 2ab + 2b^2 + 2bc + 2ac - 2bc =
2a^2 + 2b^2 - 4ab + 2ac + 2ac =
2(a^2 + b^2 - 2ab + ac)