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February 9th, 2013, 09:38 AM  #1 
Senior Member Joined: Sep 2010 From: Oslo, Norway Posts: 162 Thanks: 2  What is the correct way to apply quadratic formula?
Hello, I have this equation which I want to solve for variable : This is the Quadratic equation which I was taught in school: So I substitute the a, b and c: The problem is that Wolfram Alpha says the above is incorrect, and this is correct: Click here to see the solution at Wolfram Alpha I would like to learn why Wolfram Alpha is saying this. What do you think? Thank you for your time. Kind regards, Marius 
February 9th, 2013, 10:13 AM  #2 
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,209 Thanks: 517 Math Focus: Calculus/ODEs  Re: What is the correct way to apply quadratic formula?
You need to put your equation in standard form first: Now, you can see: 
February 9th, 2013, 10:59 AM  #3 
Senior Member Joined: Sep 2010 From: Oslo, Norway Posts: 162 Thanks: 2  Re: What is the correct way to apply quadratic formula?
Thanks.M

February 9th, 2013, 07:09 PM  #4  
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 13,802 Thanks: 970  Re: What is the correct way to apply quadratic formula? Quote:
2y = 2vtk  gt^2 Then: gt^2  2vkt + 2y = 0 Get my drift?  
February 12th, 2013, 06:28 AM  #5  
Senior Member Joined: Sep 2010 From: Oslo, Norway Posts: 162 Thanks: 2  Re: What is the correct way to apply quadratic formula? Quote:
I was looking at the dimensions in the result, and I cannot get them to match. This looks right What about this? Everything but the one m cancel out, and I am left with: Where did I go wrong? Thanks M  
February 12th, 2013, 07:21 AM  #6 
Global Moderator Joined: Dec 2006 Posts: 20,105 Thanks: 1907 
You incorrectly replaced "±" with "*" early on.

February 12th, 2013, 07:34 AM  #7 
Senior Member Joined: Sep 2010 From: Oslo, Norway Posts: 162 Thanks: 2  Re: What is the correct way to apply quadratic formula?
Skipjack, thank you so much! Now everything works out in my lovely mathematics Thank you!M 
February 13th, 2013, 05:48 AM  #8 
Senior Member Joined: Sep 2010 From: Oslo, Norway Posts: 162 Thanks: 2  Re: What is the correct way to apply quadratic formula?
Another question: When I am picking , and , I have the choice to pick the inverted set of numbers, because the right hand side of the standard form is 0 anyway. Are there any implications of doing this? I think so, at least it seems that for one set of numbers I may end up with a complex number as the result, but not in the other. For example, I suspect in the case of: may not always be equal to in the case of: Is this the case? If so, what is the correct way to pick the sign of , and ? Thank you for your time. Kind regards, Marius 
February 13th, 2013, 06:52 AM  #9 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,900 Thanks: 1094 Math Focus: Elementary mathematics and beyond  Re: What is the correct way to apply quadratic formula? 
February 13th, 2013, 07:02 AM  #10  
Senior Member Joined: Sep 2010 From: Oslo, Norway Posts: 162 Thanks: 2  Re: What is the correct way to apply quadratic formula? Quote:
 

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