An identity is an equation that is true regardless of what values are substituted in for its variables.
A conditional equation is an equation that is true only for certain values of its variables.
Isolating a variable means rearranging and modifying an equation, according to the rules of algebra, so that a variable is all by itself on one side of the equation. If we started off with the equation, we could add to both sides of the equation to end up with . The variable is now isolated.