Rules for removing brackets. Chapter I review

An expression joined by plus and minus signs is called an algebraic sum, and it can also be written as a sum: 5 - 9 + 4 = 5 + (-9) + 4. If a plus sign stands before a bracket, we drop the bracket and keep the sign of every term inside: a + (b - c) = a + b - c. If a minus sign stands before a bracket, the sign of every term inside is reversed: a - (b - c) = a - b + c. With nested brackets we open them from the inside outwards. Conversely, when enclosing terms in brackets, a plus before the bracket keeps the signs, and a minus reverses all of them: a - b - c = a - (b + c).