Using the function f(x) = 2x + 7 find the following: (show your work) 1. f(x) = 13 2. f(x)=21 to use function notation we either replace the x in the equation or the f(x) in the equation. to find f(2) we replace the in the equation with and then solve for f(x). to find f(x)=2 we replace the in the equation with and then solve for x.

Our function for these problems is f(x)=2x+7.

To find f(x)=13 we will set our first function equal to 13.
2x+7=13

Then we will solve for x.
2x+7=13
2x+7-7=13-7
2x=6
2x/2=6/2
x=3

To find f(x)=21 we will set the first function equal to 21.
2x+7=21

Now we will solve for x.
2x+7=21
2x+7-7=21-7
2x=14
2x/2=14/2
x=7

Now, let's look at the fill-in the blank part. 
To find f(2), we replace the x in the equation with 2 and solve for f(x).
To find f(x)=2, we replace the f(x)  in the equation with 2 and solve for x.