Distance Formula

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August 25th 2010, 09:19 PM
GLAMX

Distance Formula

I'm really having a hard time with this. It deals with distance formula.

http://i35.tinypic.com/2j5hztf.jpg

As you can see from that picture, I tried solving the problem and got 117 as an answer. But my teacher told me the answer was 3√13 but I have no idea how.

Please elaborately explain to me how I could arrive to the correct answer. Thank You
August 25th 2010, 09:30 PM
pickslides

$\sqrt{117}= \sqrt{9\times 13} = \sqrt{9}\sqrt{ 13}= 3\sqrt{ 13}$
August 25th 2010, 09:35 PM
MacstersUndead

Quote:

Originally Posted by GLAMX

I'm really having a hard time with this. It deals with distance formula.

http://i35.tinypic.com/2j5hztf.jpg

As you can see from that picture, I tried solving the problem and got 117 as an answer. But my teacher told me the answer was 3√13 but I have no idea how.

Please elaborately explain to me how I could arrive to the correct answer. Thank You

Actually sqrt(117) = 3*sqrt(13). However, although it is correct, it is not in the form the teacher expects. You need to factor out squares when possible. It's actually not that bad. You probably will only need to check 1, 4, 9, 16, 25, 36, 49 anyway.

Now, 117 = 9 * 13, so
sqrt(117) = sqrt(9*13)

but. we know sqrt(a*b) = sqrt(a)sqrt(b) [exponent rule], so

sqrt(9*13) = sqrt(9)*sqrt(13) = 3 * sqrt(13), and we are done.
August 25th 2010, 10:11 PM
GLAMX

Quote:

Originally Posted by pickslides

$\sqrt{117}= \sqrt{9\times 13} = \sqrt{9}\sqrt{ 13}= 3\sqrt{ 13}$

Thank you. This was very helpful. Just one more question, the 9 and 13, does it have to be those specific numbers? Or can they be two numbers that equal to 117?
August 25th 2010, 10:17 PM
pickslides

You have to find a factor of 117 that is a square number.

I.e. $1^2 = 1, 2^2 = 4, 3^2= 9 , 4^2=16, \dots$

Factoring into 2 numbers that aren't square will not have the desired affect.