When a question asks you to "evaluate" a situation, you are most likely being asked to find a numerical answer. The process is simple. Replace the variable in the expression or equation, with the numerical value you are given, and simplify the result.

 When evaluating an expression: Remember to follow the proper order of operations and to watch out for those pesky negative signs. Placing a set of parentheses around the value being substituted will help you avoid errors with signs.

Numeric Substitutions:
Evaluate 2x - 3, when x = 4.

Replace x with 4 and simplify.

2(4) - 3 = 8 - 3 = 5 Answer

Evaluate x2 - 1, when x = 5.

Replace x with 5 and simplify.

(5)2 - 1 = 25 - 1 = 24 Answer

Evaluate a2 + a, when a = 3.

Replace all values of a with 3 and simplify.

(3)2 + (3) = 9 + 3 = 12 Answer

Evaluate 6x + 3y, when x = 2 and y = 5.

Notice the use of two variables. Replace each and simplify.
6(2) + 3(5) = 12 + 15 = 27 Answer

Evaluate x3 + 3x2 - 2x - 5, when x = -4.

Especially use parentheses when working with negative values.

(-4)3 + 3(-4)2 - 2(-4) - 5 = -64 + 48 + 8 - 5 = -13 Answer

Evaluate a2b + a, when a = -3 and b = 2.
 Do NOT write: -32(2) + (-3) as this is -9(2) + (-3) = -21

Parentheses are needed in this problem.

(-3)2(2) + (-3) = 18 + (-3) = 15 Answer

Algebraic Substitutions:

It may be the case that you will be asked to evaluate an expression using another expression.
Don't panic!!! Just follow the same process as you did when evaluating for a number.

Evaluate x2 + 2x - 4, when x = 2a.

Remember to use parentheses!

(2a)2 + 2(2a) - 4 = 4a2 + 4a - 4 Answer

 Evaluate 3x + 10 when x = 3m + 15 Remember to use parentheses! 3(3m + 15) + 10 = 9m + 45 + 10 = 9m + 55 Answer

The graphing calculator can also be used to evaluate expressions.
Click on the link at the right to see the possibilities.