If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Adding the opposite with integer chips

Use integer chips to explore the conjecture that subtracting a number gives the same result as adding the opposite of the number. Created by Sal Khan.

Want to join the conversation?

Video transcript

- [Instructor] So let's use integer chips again to start exploring a little bit more when we deal with negative numbers. So let's say we wanted to compute what negative one minus seven is. See if you can pause this video and figure that out using integer chips. Well, let's do this together. So we're starting with negative one. We could represent negative one as just one integer, one negative integer chip, but we need to subtract seven, positive seven from that. We have no positive integer chips here, so, and we need to have at least seven positive integer chips in order to subtract seven. So how could we get some positive integer chips? Well, we can just add pairs of negative and positive integer chips. So if I add one negative integer chip and I add one positive integer chip, just like that, this is still negative one over here because these two integer chips are going to cancel each other out. So let me just do that seven times. So let me just do this. So that's two, three, four, five, six and seven. And then I just have to add the corresponding positive integer chips three, four, five, six and seven. So notice, what I just wrote, this is just another way of writing negative one. But I wrote it this way because I can actually subtract out positive seven now from this. So now let's subtract out positive seven. So subtract out one, two, three, four, five, six, seven. And then what are we left with? Well, we're left with all of this business right over here. And what is that? That's one, two, three, four, five, six, seven, eight. This is equal to negative eight. Now that's interesting by itself, but you might notice something. What I have left over when I take a negative one and I subtract positive seven from that, I'm left with essentially the equivalent of negative one and negative seven. So another way of writing what we just have left over here is I have negative one is that one negative integer chip right over there. And then I have negative seven, these seven negative integer chips right over there. So you could also view this as the same thing as negative one plus negative seven. And so this makes us think about something. Is it true that if I subtract a positive, that's the same thing as adding the inverse of that positive, adding, in the case of a positive seven, in the case of subtracting a positive seven, that's gonna be the same thing as adding a negative seven? Interesting. And let's see actually if it works the other way around. So let's see what happens when we subtract a negative. So if we have negative three minus negative five, maybe, maybe this is the same thing as negative three plus the opposite of negative five, which would be positive five. Let's see if these two things actually amount to be the same thing. So let's just start with this first one up here. We're gonna start with negative three, so that gives us three negative integer chips. So negative one, negative two, negative three. Now if we wanna subtract out negative five, if we wanna take away five negative integer chips, well we need more negative integer chips here. We need at least two more negative integer chips. So if we have two more negative integer chips, we're not changing the value of that if we have two more positive integer chips. What I have depicted here is still negative three because that and that cancel out. And so this is still the number negative three being represented, but I added these two pairs because now I can subtract out five negative integer chips. That's what negative five represents. These top four negative integer chips, there's five of 'em, I can take 'em all away. That's subtracting out a negative five. And what am I left with? What I'm left with is just these two positive integer chips. So this is going to be equal to positive two. Well, that's interesting because that's kind of feeling very similar to what we have here. If we start with negative three, so negative one, negative two, negative three, and I add a positive five, so five positive integer chips, one, two, three, four and five. Well, we already know that that cancels with that, that cancels with that, that cancels with that. This is the equivalent of positive two. And what I just did here on both sides, this isn't a proof that this will always work, but hopefully this gives you an intuition that it does seem to work. And I will tell you that without giving you the full proof that it actually does always work, that it is actually the case that if you subtract a number, it's the same thing as adding the opposite of that number. If you subtract a number it's the same thing as adding the opposite of that number.