Word problem

Question

Consider the function f(x) = x2 + 3x − 7. Find the value of f(x) when x = 3 and select the correct answer below.

5
8
11
18

Answer 1

A function is really just a machine.  It takes something in (one or more "independent variables"), and it gives something back (the "dependent variable") as a result.  Generally, the output depends on the input.

Finding the value of a function for a specific independent variable is simply a matter of substituting the value of the variable into the function definition.  So in this case:

 

f(x) = x² + 3x − 7

 

Saying "The value of f(x) when x = 3" is the same as saying "f(3)", so...

 

f(3) = 3² + 3*3 - 7 = 9 + 9 - 7 = 11

 

So the answer is 11

 

 

Answer 2

f(x) = x²+3x-7

To find f(3) just plug in 3 for x in the equation.

f(3)= 3²+3(3)-7

      = 9+9-7

      = 11