In this video we want to show you how to use this button right here, the STO with an arrow. It's a store, it's going to store values. In the TI-84 calculator how can we use this button in order to help us evaluate the values of certain functions. So in order to illustrate this let's use this example over here. So suppose we want to estimate the limit as x goes to seven of one over x minus seven, and let's just do this numerically. So this is a two-sided limit, so in order to evaluate this limit we would need to look at the right-hand limit and the left-hand limit.
So the right-hand limit, we would want to use x values to substitute into this function that are very close to seven but on the right side of seven. So I've chosen 7.1, 7.01, 7.001, and 7.0001. How can I use this store button in order to help me calculate these function values for those given values of x? Well we just stay here on this home screen, and I type in the value that I want to first store. So let's store 7.1. So 7.1, we're going to store that, so I click on the STO arrow button and we're going to store that as x up here. So I'm going to click the x, t, theta n button. And then I hit enter, and now my calculator from this home screen thinks that x is 7.1. And we could find that out just by hitting x and then enter and it shows 7.1. So it's a way for you to store values in the calculator for x. And now you have to type in the function that you want it to evaluate. So i want to evaluate one divided by parenthesis x minus seven, close my parentheses. So again remember whenever you have a denominator we need to put parentheses around the entire denominator. So what's happening here is the calculator thinks that x is 7.1. So it's going to take 7.1 and substitute it into this expression when I hit enter. So now you see we get 10. So when x is 7.1, and I substitute that into this function, 10 is the output. Now let's see what we would get for 7.01. So we would want to say 7.01, store it in for x, I have to redefine what x is, and now my calculator does think that x is 7.01. Now I want to quickly bring up this function that I already typed in and I did it two entries ago right. So I'm going to click second, enter, and it brings up the last entry, so that's why my what just came up matches what came up above the dotted line, but I'm going to do that one more time and watch this, it will give me what I entered above that one. So because I wanted two entries above where I am right there's two dotted lines above where the cursor currently is, I had to hit second enter, second, enter, twice to access that. And now when I hit enter, what my calculator did for me was took 7.01. That was the x value and it substituted into this function, and I get 100 out. So when x is 7.01, then the function one over x minus seven has a value of 100. So you might be catching on by now, now we're going to substitute 7.001. We're going to store that for x, hit enter so that it actually stores it right, that kind of locks it in, and now I'm going to do second, enter, second, enter, again so that I get that entry two entries above it, hit enter, and you get a thousand. And now you can do 7.0001, store as x, hit enter so it locks in that value for x, hit second, enter, second, enter, again, and now you just hit enter and it gives you 10000. So it evaluated that x value of 7.0001 into the function we get 10000. So what we can see here is that we had 10 and then 100 and then a thousand and then 10000, so I could kind of easily see here that the function values are getting larger and larger and larger as I come into seven on the right side. So just kind of finishing up this right side problem then you we would see that the limit as x goes to seven on the right side of one over x minus seven tends toward positive infinity, because the closer and closer and closer I get to seven on the right side, the function values get larger. So for this problem I'm going to stop right there, because I really just wanted to demonstrate how you can use the store button to store values for x.