Watch the video below to see some examples of evaluating functions.
To practice evaluating functions at certain values, I’ve decided to choose these three functions: f of x equals three x plus four; g of x equals two x plus five; and h of x equals seven x plus one.
So three separate functions, three separate equations that we are going to use in this practice.
So when we evaluate a function, what we are actually doing is we’re doing substitution. That’s really all it is. So if I asked you to find f of two, that means, plug in two for x. So we’re going to substitute two for x and solve.
So let’s do that. All right, the original function says three times our x--we’re not going to use x, we’re going to put parenthesis there for now. Three times something plus four. What is that something? That something is what I put right here. That’s a two. So if I work this out, three times two is six plus, and we have our plus four, which is ten. So f of two in this case is equal to ten.
Let’s try one with our h function. So if I had h of three, I would use this one which says seven times something plus one. That something in this case is this value right there, three. Seven times three is twenty-one plus one gives me twenty-two. So h of three is equal to twenty-two.
So what I want you to do right now is I want you to work on these three equations. These three questions, I want you to answer. That is, f of three, g of two, h of one. So I want you to pause the video right now. Look at the left side over here and find these three values for me using these three functions.
All right, now that you’re back, I’ll reveal the answers f of three--I’m using the f function--which is this one, so I used three times something plus four. What’s that something right here? That’s that value of three. Three times three is nine plus four is thirteen. So f of three, in this case, is thirteen.
So let’s try this g function. This is the g function. So I need two times something plus five. What’s that something? That something is our two again. Two times two is four plus five is nine.
So let’s do the same with the h. H is seven times something plus one. What’s that something? That something is one. Which says eight--excuse me, seven plus one is eight. All right so there is a quick review evaluating linear functions.
