The Commonwealth was the republican government which ruled first England and then the whole of Britain and Ireland during 1649 - 1653 and 1659 - 1660. The term is also loosely used to describe the system of government during the whole of 1649 - 1660, the years of the Interregnum[?], although during 1653 - 1659, the government is properly called The Protectorate and took the form of direct personal rule by Oliver Cromwell, the Lord Protector.
... will make it a perfect square trinomial of the form x2 + 2xy + y2. Since "2xy" in this case is (b/a)x, we must have y = b/(2a), so we add the square of b/(2a) to both ...