Definition
Evaluate an expression
To evaluate an expression means to find its value for the given variable values.
What it means
First replace every variable with the number you were given. Use parentheses around substituted negative numbers so the signs stay clear. Then calculate in the correct order until one value remains.
Remember it
Evaluate means plug in the values, then work the calculation through.
Example
Evaluate 2x² + y when x = 3 and y = 2. Substitute: 2(3)² + 2. Calculate the power first: 2 × 9 + 2 = 20.
Watch for
Simplifying changes an expression into an equivalent form; evaluating produces a value for specified variable values.
Common mix-up
When substituting a negative number, use parentheses: if x = −2, then x² becomes (−2)², not −2².
Exact meaning
To evaluate an expression is to determine its numerical value by replacing each variable with its given value and then carrying out the operations according to grouping and order-of-operations rules.