# An algebra question

• Jun 16th 2010, 10:12 AM
econlover
An algebra question
Question: Simplify the following expression.

(2x5^n)^2 + 25^n

this whole equation is divided by

5^n

• Jun 16th 2010, 10:28 AM
earboth
Quote:

Originally Posted by econlover
Question: Simplify the following expression.

(2x5^n)^2 + 25^n

this whole equation is divided by

5^n

1. Use the laws of powers:

$\displaystyle \frac{(2 \cdot 5^n)^2 + 25^n}{5^n} = \frac{4 \cdot 5^{2n} + 5^{2n}}{5^n}= \frac{5 \cdot 5^{2n}}{5^n}=5 \cdot 5^n = 5^{n+1}$
• Jun 16th 2010, 10:33 AM
econlover
slight question
Thanks.

I understand most of it but how did you move along from the 1st step of your answer to the second one

that is, in specific terms, where did the 4 go?
• Jun 16th 2010, 10:39 AM
SpringFan25
considering the numerator (top of fraction) only:
$\displaystyle 4 . 5^{2n} + 5^{2n} = (4+1).5^{2n} = 5 \times 5^{2n} = 5^{2n+1}$
• Jun 16th 2010, 10:41 AM
econlover
Thanks for the message. But I guess you misinterpret the sign of this "."

It is not 4.5 (4 decimal 5) but 4 . 5 meaning 4 x 5 = 4 times 5

Hope this clears up the misconception
• Jun 16th 2010, 10:47 AM
econlover
Still don't understand this step. Where did the 1 come from ? What about the positive sign?

Can someone explain? Thanks!
• Jun 16th 2010, 11:18 AM
SpringFan25
it is only factorising. i was not interpreting your dot as a decimal.

in general:
4x + x = (4+1)x = 5x

You have
$\displaystyle 4 \times 5^{2n} + 1 \times 5^{2n}$ = $\displaystyle 5 \times 5^{2n}$

Which says: "4 lots of $\displaystyle 5^{2n}$ plus 1 lot of $\displaystyle 5^{2n}$" equals "5 lots of $\displaystyle 5^{2n}$"
• Jun 17th 2010, 01:03 PM
bjhopper
Quote:

Originally Posted by econlover
Question: Simplify the following expression.

(2x5^n)^2 + 25^n

this whole equation is divided by

5^n

Hi ecolover,

follow exp rules carefully. the 4 disappears naturally because 4+1 =5 You should get it from this clue

bjh