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Current time:0:00Total duration:2:25

Graphing linear equations — Basic example

Video transcript

- [Narrator] The value of a bond on January 1st, 2014 is $1,000. Each year the value of the bond increases linearly by $75. After one year it's going to be $1,075, after another year, it's gonna be $1,150, so on and so forth. Which graph below represents v, the dollar value of the bond, as a function of t, the number of years after January 1st, 2014? Well there's a couple ways to think about it. What's the value of the bond when t equals zero? When t equals a zero that means that we are at January 1st, 2014. We are no years after January 1st, 2014, so when t equals zero, we should get the $1,000 value of our bond. So let's see, this, this choice has that. At t equals zero, our bond is worth $1,000. This one, at t equals zero, I don't know, it doesn't even, I don't even see what the value of the bond is, so I would rule this one out. This one, at t equals zero, the value of our bond is $1,000. This one, at t equals zero, our value of our bond is $500, so I would rule this one out, as well. So, the two that we're left with, this one and this one, they start in the right place, but let's see how fast they increase. So remember, every year we should be increasing by $75, or you could say every two years, we should be increasing by $150 or every three years, we should be increasing by $225. So let's see, here it's, I'm just gonna try to eyeball it, so after two years, we should increase by about $150, and that doesn't look inconsistent because one whole block in the vertical axis is $500. So let's think, after three years, we should be $225. We should be, so that actually looks a little bit less than, a little less than half of 500, so this one is looking pretty good. Let's look at this choice right over here. This one's actually a little bit clearer. It looks like in two years, we've increased almost $500, which means, we're increasing nearly $250 per year. You see that in one year, we're almost, or it looks like we're over, even if we spend more than $200, so this one is increasing too fast, so we rule this one out, and this one looks close enough. It looks like it's consistent with $75 increase per year, and once again, we're just eyeballing it, but it looks, it looks pretty good, and this one is way off, and these two just started in the wrong place, so I would definitely go with this one.