Answer:
To evaluate a variable expression means to find the value of the expression when the variable is (or variables are) replaced by a number (or numbers).
Here is a variable expression: 3x+7.
To evaluate this expression when x=2 mean to substitute 2 in place of x, and find the number (the value). [see note below]
3(2)+7=6+7=13.
When x=2, the expression has a value of `13.
If we evaluate the same expression when x=10, we get:
3(10)+7=30+7=37.
Here's a variable expression with two variables : 3x−2y
In order to evaluate this expression, we'll need values (numbers) for both x and y.
Evaluate the expression 3x−2y when x=4 and y=5
3(4)−2(5)=12−10=2
If we change the values to x=5 and y=4, we get
3(5)−2(4)=15−8=7.
Note:
To avoid saying exactly the same thing over and over, we use the following to mean the same thing:
evaluate the expression when x=2
evaluate the expression for x=2
evaluate the expression at x=2
evaluate the expression assuming x=2
evaluate the expression if x=2
Also
If there is only one variable in an expression, we don't always need to mention it:
evaluate the expression for 2
evaluate the expression at 2