To evaluate an algebraic expression, take the given values for the variables, and plug them in to see what the result is. Evaluating an algebra expression is the reverse of solving an equation. Make sure to follow the order of operations at all times; otherwise, the result could be incorrect.
The order of operations is parentheses, exponents, multiplication, division, addition and subtraction. For an example expression, take 4x^2 + 3x + 9 where x = 5. Plugging the required value into the equation results in 4(5)^2 + 3(5) + 9. Exponents come first. When simplified, the expression is 4(25) + 15 + 9. Performing the required arithmetic yields the result of this expression to be 124. Remember that if a parenthetical term has an exponent outside it, you should simplify the term first before applying the exponent; exponents do not distribute over addition.
Evaluating algebraic expressions provides one method of solving linear or quadratic equations. By substituting a given value for x, it's possible to find the corresponding point for y. For example, solving y = 3x + 2 when x = 3 leaves y as 11. By plugging in a different value for x, you can get another point on the line described by the equation.