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## Algebra (all content)

### Course: Algebra (all content) > Unit 11

Lesson 15: Equivalent forms of exponential expressions# Rewriting exponential expressions as A⋅Bᵗ

Sal simplifies the expression 10*9^(0.5t+2)*5^(3t) as 810*375^t.

## Want to join the conversation?

- At2:49Sal gets the answer for 9^1/2 as 3. How does that work? How do you raise a number to a fractional exponent?(10 votes)
- 9^(1/2) is equivalent to the square root of 9. For a fractional exponent, the denominator is the nth root, and the numerator is the power. For example 9^(3/2) is sqrt(9^3).(39 votes)

- Anyone else find that the video doesn't prepare them to tackle the practice exercises? There seems to be a missing step.(33 votes)
- Yes that's true,but I don't think that is important(0 votes)

- The practice problems have nothing to do with the video...we were never taught how to do the practice problems.(27 votes)
- Hello, I have been having a problem in the next practice. I don't know how to do problems that look similar to this one;

(5/2)^x + (5/2)^(x+3) = A * (5/2)^x

I know that this simplifies into,

(5/2)^x + (5/2)^x * (125/8),

but I have no idea how to get the expression,

(5/2)^x ((125/8) + 1).(22 votes)- Your simplified equation is:

(5/2)^x + (5/2)^x*(125/8)

Everything is multiplied by an invisible one.

(5/2)^x*1+(5/2)^x*(125/8)

If it is this number**_+ this number*__*we can add the*_+__*and multiply it by this number. So when it is simplified the end expression is:

this number*(*_+__*).

If you apply it to this expression, the end result is:

(5/2)^x*((125/8) + 1).

I hope this explanation isn't to confusing.

If you need help understanding it, please comment.(8 votes)

- Is anyone able to recommend any videos from any source that explains the concepts in the practice exercises? Like rewriting exponential expressions in a certain way? I really need instructions on how to do this, not just how to solve 1 particular problem like these videos show. In this video, he just happened to get lucky in finding the correct form that the question was asking. How do you manipulate an expression to the proper form without taking random shots in the dark? Thanks for any help!(16 votes)
- This was the only video I could find that seemed somewhat helpful: https://www.youtube.com/watch?v=gyz0vyykiSw(12 votes)

- Sal said 9 ^ 1/2 = 3. Is there any way to express like 9 ^ (something) = -3 ?(6 votes)
- Only imaginary numbers can satisfy that equation.(8 votes)

- I got nothing from the video, can someone give me a brief-but yet understandable explanation of the concept Sal is trying to explain? Thank you and have a great day! :D(8 votes)
- Howdy Joseph,

When writing an exponential expression it is usually the most convenient to have it in the form of A * B^t, where A and B are any real numbers.

In this video, Sal was giving examples of using some exponent properties to help show how to rewrite exponential expressions.**Exponential Propertes**

Here are some exponential properties that you should be familiar with.

a^(bc) = (a^b)^c // or vice versa

a^b * a^c = a^(b + c)

a^b / a^c = a^(b - c)

a^c * b^c = (a*b)^c

Once you know those exponential properties, we can use them to simplify our exponential expressions to a more simpler form, preferably A*B^t.

Now that you know what Sal is trying to do, it may be advisable to rewatch the video and get some practice rewriting exponential expressions.

Happy learning! :-)(10 votes)

- why cant someone just make update videos so we can actually do the practice questions instead of banging our heads against the wall(12 votes)
- I don't feel the video for "equivalent forms of exponential expressions" is adequate preparation for the practice problems. Perhaps more examples are needed in the video.(9 votes)
- Agreed, the explanations also don’t show how you can factor out something with the same base but different exponents. Maybe the video is elsewhere but this video definitely doesn’t explain.(6 votes)

- Why does one of the practice questions in this section include rewriting a number as a new base, number bases haven't been covered yet. This whole exponents section has a few gaps and might be out of order.(11 votes)

## Video transcript

- [Voiceover] What I
hope to do in this video is get some practice simplifying some fairly hairy exponential expressions. So let's get started. Let's say that I have the expression 10 times nine to the t over two plus two power, times five to the three t. And what I wanna do is simplify
this as much as possible, and preferably get it in the form of A times B to the t. And like always, I encourage
you to pause this video and see if you can do this on your own using exponent properties, your knowledge, your deep knowledge of
exponent properties. All right, so let's work
through this together, and it's really just about
breaking the pieces up. So 10, I'll just leave that as 10 for now, there doesn't seem to be much to do there. But there's all sorts
of interesting things going on here. So nine to the t over two, plus two, so this right over here,
I could break this up, using the fact that, and I'll just write the properties over here. If I have nine to the a plus b power, this is the same thing as nine to the a, times nine to the b power. And over here I have
nine to the t over two, plus two, so I could rewrite this as nine to the t over two power, times nine squared. All right, now let's move over to five to the three t. Well, if I have a to the bc, so you could view this as
five to the three times t, this is the same thing as a to the b, and then that to the c power. So I could write this
as, this is going to be the same thing as five to the third, and then that to the t power. And the whole reason I did that is well this is just going to be a number, then I'm going to have
some number to the t power. I want to get as many things just raised to the t power as possible, just to see if I can simplify this thing. So this character right
over here is going to be 81. Nine squared is 81. Five to the third power, 25 times five, that's 125. So we're making good progress and so the only thing we really have
to simplify at this point is nine to the t over two. And actually let me do that over here. Nine to the t over two. Well that's the same thing as nine to the one half times t. And by this property right over here, that's the same thing as nine to the one, nine to the one half... And then that to the t power. So what's nine to the one half? Well that's three, so this is going to be equal to three to the t power. So this right over here is three to the t power. So now this is getting interesting. So I have the 10 out front, times three to the t, Actually let me write the 81 first. 10 times 81 times three to the t, so all I did is I just swapped the order that I'm multiplying. Times 125 to the t. Times 125 to the t power. Now, the 10 times 81, I
can just multiply that out. That's going to be 810. And then what's three to the t times 125 to the t? Well this is another exponent
property at play here. Because if I have a
times b to the t power, that's a to the t times be to the t. Or another way to think about it, if I have a to the t times b to the t, that's the same thing as
a times b to the t power. And so over here I have three to the t times 125 to the t, so it's
going to be the same thing as three times 125 to the t power. So this part of it right over here, I could rewrite it as three times 125, and I'm gonna raise that
whole thing to the t power. So I'm in the home stretch. This is going to be 810, times three times 125 is 375. Times 375, to the t power. And that's about as
simplified as we can get, and we did indeed write it in the form that we hope to write it in. That a times be to the t. Where if we actually match
this form right over here, this right over here would be our A, and then our B would be the 375. So anyway, I know it looked
a little bit daunting when you first saw it, but
if you just keep saying okay let's just keep
applying some exponent properties here, let's see if I can get multiple things to the t power, and keep breaking it down
using these properties, you see that in not too many steps you get to something
that's a lot less hairy.