I understand that
But what if I have
Would that be x=2(plus/minus y) or would the -2 have to be included in the plus/minus part?
is a contraction for "x=2 or x=-2". Even though may seem a number, like y or -y, it cannot be viewed in isolation. Usually one has some proposition (i.e., an expression that is either true or false) . This means " or ". Therefore, " " and " " are the equivalent and mean "x=2y or x = -2y".