An equation is a mathematical statement such that the expression on the left
side of the equals sign (=) has the same value as the expression on the right side.
An example of an equation is - 200 - (- 600) = 400.

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. - 200 + x = 400).

The solution of an equation is finding the value of the unknown x. To find the
value of x we can use the subtractive equation property which says: The two sides of an
equation remain equal if the same number is subtracted from each side. We may also use
the additive equation property which says: The two sides of an equation remain equal
if the same number is added to each side.

Example:

x - (- 500) = 400

x + 500 = 400

x + 500 - 500 = 400 - 500

x + 0 = - 100

x = - 100

Check the answer by substituting the answer ( - 100) back into the equation.

- 100 - ( - 500) = 400