When given an algebraic expression, one of the most common things to do with it is evaluate it for some given value of the variable.
Take a look at this example to see how this works:
Let x = 12. Find the value of 2x - 7.
To find the solution, substitute 12 in place of in the given expression.
Note: In the first step of the problem, keep the substituted value in parentheses. This makes the written-out problem easier to follow, and helps avoid mistakes. (If we didn’t use parentheses and also forgot to add a multiplication sign, we would end up turning "" into "212" instead of "2 times 12!")
Evaluating an Expression
Let Find the value of
Many expressions have more than one variable in them. For example, the formula for the perimeter of a rectangle, , has two variables: length and width Be careful to substitute the appropriate value in the appropriate place.
Evaluating an Expression with Multiple Variables
The area of a trapezoid is given by the equation . Find the area of a trapezoid with bases and and height .
To find the solution to this problem, substitute the given values for variables and in place of the appropriate letters in the equation.
Let and Find the value of .
Evaluate questions 1 through 8, using and
For questions 9 through 11, the weekly cost of manufacturing remote controls is given by the formula , where the cost is given in dollars.
- What is the cost of producing 1000 remote controls?
- What is the cost of producing 2000 remote controls?
- What is the cost of producing 2500 remote controls?
To view the Review answers, open this PDF file and look for section 1.2.