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#1 2017-01-10 16:41:08

numquester
Member
Registered: 2016-12-12
Posts: 9

The quadratic formula

I came across a video in which the author explains visually how to arrive at the quadratic formula, except he skips some steps.

Here is the video:  https://www.youtube.com/watch?v=EBbtoFMJvFc

I follow it up to this point, where some steps are skipped:  https://www.youtube.com/watch?v=EBbtoFMJvFc&t=7m45s

In the video, the right side of the equation goes from: 

To: 

So I think that I can rewrite the first example like this: 

But I don't see how the a can be moved to the numerator.  Or maybe I'm approaching it all wrong.

By the way, I really like this approach to explaining math.  I never understood what 'completeing the square' actually means until I saw this video.  It seems right at home with so many of the nice explanations here at Math is Fun.

Side note:  I really appreciate the LaTeX integration in the forum.  This is nice!

Last edited by numquester (2017-01-10 16:49:17)

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#2 2017-01-10 20:37:01

bob bundy
Moderator
Registered: 2010-06-20
Posts: 7,738

Re: The quadratic formula

hi numquester

Think about how you would add two fractions.

This is what you have done:

This isn't correct.  You have to put both fractions over a common denominator and then just add the tops:

So in the formula  multiply the first fraction top and bottom by 4a

Hopefully you can see how this works now.

Bob


Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#3 2017-01-11 08:16:03

numquester
Member
Registered: 2016-12-12
Posts: 9

Re: The quadratic formula

Bob, that is a very clear explanation.  Thanks for taking the time.

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