###### Alissa Fong

MA, Stanford University
Teaching in the San Francisco Bay Area

Alissa is currently a teacher in the San Francisco Bay Area and Brightstorm users love her clear, concise explanations of tough concepts

##### Thank you for watching the video.

To unlock all 5,300 videos, start your free trial.

# Function Notation - Problem 2

Alissa Fong
###### Alissa Fong

MA, Stanford University
Teaching in the San Francisco Bay Area

Alissa is currently a teacher in the San Francisco Bay Area and Brightstorm users love her clear, concise explanations of tough concepts

Share

When you are doing function notation you don't always get the letter f sometimes you get other letters like g or h like in this problem. But it's okay you do the same process you're just going to use instead of f you are going to be using g, no big deal.

So in this first problem part a, they're telling me that instead of x stick the number 3 in there, wherever you see x you are going to right 3 instead. So I'll have g(3) is equal to 4 times 3 take away 3. That's where the x number used to be x it became 3. So go through to it evaluate g(3) is going to be 12 take away 3, g(3) is equal to 9.

Not so bad one thing that I like again about function is that you can see what your input value was in addition to seeing your output value. Let's try this one find x when g(x) is equal to 29.

Okay instead of I mean so you have this is going to work. This is my original problem g(x) equals 4x minus 3, that's my original function it tells me g(x) is 29 so instead of g(x) watch this I'm going to write 29 there instead and then I bet this is a problem you guys can solve without much difficulty.

The trick is how to set it up how to replace that g(x) piece with number 29. From there it's just like pluggy-chuggy, you guys know what to do. 32 equals 4x, x equals 8. These are kind of backwards problems, in this problem I was giving an x value and asked to evaluate to find g, this is like the reverse here I'm given g(x) as equal to its like I'm given the out put as to find the input.

So again the thing to keep in mind is that you don't always see the letters f(x) sometimes you may see g(x) or h(x) or whatever that's okay you still use the same processes. Also be aware if they are giving you an input value and asking you to find the output or if they are giving you the output like here and they're asking you to do it kind of backwards. Find that x input number.