January 27th, 2011, 09:05 AM  #1 
Newbie Joined: Jan 2011 Posts: 4 Thanks: 0  Radicals
I just wanted to know the answer to a specific question: sqrt15 sqrt21 / sqrt5 The answer I got was 9sqrt7 Any help is greatly appreciated, thank you. jrobbo 
January 27th, 2011, 09:13 AM  #2 
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,155 Thanks: 462 Math Focus: Calculus/ODEs  Re: Radicals
You are given: Since we may write this as: 
January 27th, 2011, 09:14 AM  #3 
Global Moderator Joined: Nov 2009 From: Northwest Arkansas Posts: 2,766 Thanks: 4  Re: Radicals
Since ?(15) = ?(5)*?(3), we can cancel the ?(5) from top and bottom and be left with ?(3)*?(21) = ?(3)*?(3)*?(7) = 3?(7) And Mark strikes again! 
January 27th, 2011, 09:18 AM  #4  
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,155 Thanks: 462 Math Focus: Calculus/ODEs  Re: Radicals Quote:
It never hurts to have more than one way to look at a given problem.  
January 27th, 2011, 11:28 AM  #5 
Global Moderator Joined: Nov 2009 From: Northwest Arkansas Posts: 2,766 Thanks: 4  Re: Radicals
... or more than one way to use the same "formula"!

January 28th, 2011, 09:30 AM  #6 
Newbie Joined: Jan 2011 Posts: 4 Thanks: 0  Re: Radicals
thanks guys

January 28th, 2011, 10:11 AM  #7 
Global Moderator Joined: Nov 2009 From: Northwest Arkansas Posts: 2,766 Thanks: 4  Re: Radicals
You are welcome.

February 10th, 2011, 04:13 AM  #8 
Newbie Joined: Jan 2011 From: Houston, Texas Posts: 13 Thanks: 0  Re: Radicals
I did the same thing via video on my blog and youtube, but I won't include that bit. Here's a couple of other videos about radicals and why (and when) you can use them to do what we did here in this thread. I put these before and after my solution, so they are directly related, btw. Rednecks falling in love explanation: http://www.youtube.com/user/idearella#p/u/2/jUqYlK7mPgg Having stupid addition in the mix: http://www.youtube.com/user/idearella#p/u/0/Uawf6pgGG7o 

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