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## College Algebra

# Rewriting roots as rational exponents

CCSS.Math: ,

Sal solves several problems about the equivalence of expressions with roots and rational exponents. For example, rewrite ⁶√(g⁵) as g^⅚.

## Video transcript

- [Voiceover] We're asked to determine whether each expression is equivalent to the seventh root of v to the third power. And, like always, pause the
video and see if you can figure out which of
these are equivalent to the seventh root of v to the third power. Well, a good way to figure
out if things are equivalent is to just try to get
them all in the same form. So, the seventh root of
v to the third power, v to the third power, the seventh root of
something is the same thing as raising it to the 1/7 power. So, this is equivalent
to v to the third power, raised to the 1/7 power. And if I raise something to
an exponent and then raise that to an exponent, well
then, that's the same thing as raising it to the product
of these two exponents. So, this is going to be the same thing as v to the three times 1/7 power, which, of course, is 3/7. 3/7. So, we've written it
in multiple forms now. Let's see which of these match. So, v to the third to the 1/7 power, well, that was the form that
we have right over here, so that is equivalent. V to the 3/7. That's what we have right over here, so that one is definitely equivalent. Now, let's think about this one. This is the cube root of v to the seventh. Is this going to be equivalent? Well, one way to think about it, this is going to be the same thing as v to the 1/3 power ... actually, no, this wasn't the
cube root of v to the seventh, this was the cube root of v,
and that to the seventh power. So, that's the same thing
as v to the 1/3 power, and then, that to the seventh power. So, that is the same thing
as v to the 7/3 power, which is clearly different
to v to the 3/7 power. So, this is not going to
be equivalent for all v's, all v's for which this
expression is defined. Let's do a few more of these,
or similar types of problems dealing with roots and
fractional exponents. The following equation is true for g greater than or equal to
zero, and d is a constant. What is the value of d? Well, if I'm taking the
sixth root of something, that's the same thing as
raising it to the 1/6 power. So, the sixth root of g to the fifth, is the same thing as g to the fifth, raised to the 1/6 power. And, just like we just
saw in the last example, that's the same thing as g
to the five times 1/6 power. This is just our exponent properties. I raise something to an exponent and then raise that whole thing
to another exponent, I can just multiply the exponents. So, that's the same thing as g to the 5/6 power. And so d is 5/6. Five over six. The sixth root of g to the
fifth is the same thing as g to the 5/6 power. Let's do one more of these. The following equation is
true for x greater than zero, and d is a constant. What is the value of d? Alright, this is interesting. And I forgot to tell
you in the last one, but pause this video as
well and see if you can work it out on ...or pause
for this question as well and see if you can work it out. Well, here, let's just start rewriting the root as an exponent. So, I can rewrite the whole thing. This is the same thing as one over, instead of writing the seventh root of x, I'll write x to the 1/7 power is equal to x to the d. And if I have one over
something to a power, that's the same thing as that something raised to the negative of that power. So, that is the same thing as x to the negative 1/7 power. And so, that is going to
be equal to x to the d. And so, d must be equal to, d must be equal to negative 1/7. So, the key here is when
you're taking the reciprocal of something, that's the
same thing as raising it to the negative of that exponent. Another way of thinking about it is you could view this as, you could view it as, x to the 1/7 to the negative one power. And then, if you multiply these exponents, you get what we have right over there. But, either way, d is
equal to negative 1/7.