An **equation** is a mathematical statement that has an expression on the left side of the equals sign (=) with the same value as the expression on the right side.

One of the terms in an equation may not be know and needs to be determined. Often this unknown term is represented by a letter such as "**x**".

(e.g. 5 + x = - 2)

Solving an equation means manipulating the expressions and finding the value of the unknown variables. In order to solve for the unknown variable, you must isolate the variable

To keep an equation equal, we must do exactly the same thing to each side of the equation. If we add (or subtract) a quantity from one side, we must add (or subtract) that same quantity from the other side.