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CCSS Math: 8.EE.A.1

- [Narrator] Let's get some practice with our exponent properties, especially when we have integer exponents. So, let's think about what
four to the negative three times four to the fifth power is going to be equal to. And I encourage you to pause the video and think about it on your own. Well there's a couple of ways to do this. See look, I'm multiplying two things that have the same base, so this is going to be that base, four. And then I add the exponents. Four to the negative three plus five power which is equal to four
to the second power. And that's just a straight
forward exponent property, but you can also think about why does that actually make sense. Four to the negative 3 power, that is one over four to the third power, or you could view that as one over four times four times four. And then four to the fifth, that's five fours being
multiplied together. So it's times four times four times four times four times four. And so notice, when you multiply this out, you're going to have five
fours in the numerator and three fours in the denominator. And so, three of these in the denominator are going to cancel out with three of these in the numerator. And so you're going to be left with five minus three, or negative three plus five fours. So this four times four is the same thing as four squared. Now let's do one with variables. So let's say that you have A to the negative fourth power times A to the, let's say, A squared. What is that going to be? Well once again, you have the same base, in this case it's A, and so
since I'm multiplying them, you can just add the exponents. So it's going to be A to the
negative four plus two power. Which is equal to A to
the negative two power. And once again, it should make sense. This right over here, that is one over A times A times A times A and then this is times A times A, so that cancels with that,
that cancels with that, and you're still left
with one over A times A, which is the same thing as
A to the negative two power. Now, let's do it with some quotients. So, what if I were to ask you, what is 12 to the negative seven divided by 12 to the negative five power? Well, when you're dividing, you subtract exponents if
you have the same base. So, this is going to be equal to 12 to the negative seven minus negative five power. You're subtracting the bottom exponent and so, this is going to
be equal to 12 to the, subtracting a negative is the same thing as adding the positive, twelve to the negative two power. And once again, we just
have to think about, why does this actually make sense? Well, you could actually rewrite this. 12 to the negative seven divided by 12 to the negative five, that's the same thing as
12 to the negative seven times 12 to the fifth power. If we take the reciprocal
of this right over here, you would make exponent positive and then you would get
exactly what we were doing in those previous examples with products. And so, let's just do one more with variables for good measure. Let's say I have X to the
negative twentieth power divided by X to the fifth power. Well once again, we have the same base and we're taking a quotient. So, this is going to be X to
the negative 20 minus five cause we have this one right
over here in the denominator. So, this is going to be equal to X to the negative twenty-fifth power. And once again, you could
view our original expression as X to the negative twentieth and having an X to the
fifth in the denominator dividing by X to the fifth is the same thing as multiplying by X to the negative five. So here you just add the exponents and once again you would get X to the negative twenty-fifth power.