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. An example of an equation is 2 + (- 6) = - 4.

One of the terms in an equation may not be known and needs to be determined. The unknown term may be represented by a letter such as x (e.g. 2 + x = - 4). The equation is solved by finding the value of the unknown x that makes the two sides of the equation have the same value.

Use the subtractive equation property to find the value of x in addition equations. The subtractive equation property states, "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:

Check the answer by substituting (9) for x in the original equation. The answer is correct if the expressions on each side of the equals sign have the same value.

-5 + 9 = 4
4 = 4 (Correct!)

Example:

Check the answer by substituting (-1) for x in the original equation. The answer is correct if the expressions on each side of the equals sign have the same value.

-1 - (-5) = 4
4 = 4 (Correct!)