# Homework Help: Explanation of a simple exponent rule in a derivative problem needed

1. Aug 20, 2011

### AwesomeSN

Explanation of a "simple" exponent rule in a derivative problem needed

After differentiation, I get this : 9(t-2/2t+1)8 * 5/(2t+1)2

Now this simplifies into 45(t-2)/(2t+1)10

Now, I am wondering what the property is that combines the exponent from the top with the bottom to get an power of 10 in the simplified form.

*Note. the t-2/2t+1 is t-2 over 2t+1, the 5/(2t+1)2 is 5 over (2t+1)2, and the 45(t-2)/(2t+1)10 is 45(t-2) over (2t+1)10.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Aug 20, 2011

### Pi-Bond

Re: Explanation of a "simple" exponent rule in a derivative problem needed

From the rules of exponents:

$a^n a^m = a^{n+m}$

3. Aug 20, 2011

### ArcanaNoir

Re: Explanation of a "simple" exponent rule in a derivative problem needed

if you start with $$9 (\frac{t-2}{2t+1})^8 * \frac{5}{(2t+1)^2}$$
then you can write $$9 \frac{(t-2)^8}{(2t+1)^8}* \frac{5}{(2t+1)^2}$$
and then you add the exponents when multiplying like bases, thus getting $$45 \frac{(t-2)^8}{(2t+1)^{10}}$$

Note that $$(2t+1)^8(2t+1)^2=(2t+1)^{10}$$

edit:
boo, pibond beat me cause I'm slow at latex! :P

Last edited: Aug 20, 2011
4. Sep 11, 2011

### AwesomeSN

Re: Explanation of a "simple" exponent rule in a derivative problem needed

Thank you. I was aware of the rule for exponents, but applying the power of 8 to both the numerator and denominator escaped me, now it all makes sense!