Results 1 to 5 of 5

Thread: quadratic formula derived

  1. Sep 6th, 2003, 03:18 PM #1
    Sneeden
    Sneeden is offline

    Thread Starter
    Hyperactive Member Sneeden's Avatar
    Join Date
    Oct 2001
    Location
    Sneedville
    Posts
    258

    quadratic formula derived

    A co workier of mine was asking about how this formaula was come up with. I could work it backwards to the Ax^2 + Bx + c =0, but when trying to go the other way, I could not explain where the number 4 comes from? Is it from "completeing the square"? or what?
    Reply With Quote Reply With Quote
  2. Sep 6th, 2003, 05:01 PM #2
    nishantp
    nishantp is offline
    Frenzied Member nishantp's Avatar
    Join Date
    Jan 2001
    Location
    Where you least expect me to be
    Posts
    1,375
    I learnt this in grade 10. Its just a bunch of transformations. I'll dig it up and post it later.
    You just proved that sig advertisements work.
    Reply With Quote Reply With Quote
  3. Sep 6th, 2003, 05:07 PM #3
    nishantp
    nishantp is offline
    Frenzied Member nishantp's Avatar
    Join Date
    Jan 2001
    Location
    Where you least expect me to be
    Posts
    1,375
    As it turns out, my grade 10 math teacher wasnt the only one who knew.

    http://mathforum.org/library/drmath/view/53153.html

    and here http://library.thinkquest.org/29292/...lving/3derive/
    You just proved that sig advertisements work.
    Reply With Quote Reply With Quote
  4. Sep 6th, 2003, 05:11 PM #4
    Guv
    Guv is offline
    Frenzied Member
    Join Date
    Jul 1999
    Location
    Huntingdon Valley, PA 19006
    Posts
    1,151
    ax2 + bx + c = 0

    x2 + bx/a + c/a = 0

    x2 + bx/a = -c/a

    x2 + bx/a + b2/4a2 = b2/4a2 - c/a

    Bolded term makes left side a perfect square.

    (x + b/2a)2 = b2/4a2 - 4ac/4a2

    x + b/2a = SquareRoot( b2/4a2 - 4ac/4a2 )

    x + b/2a = SquareRoot( b2 - 4ac)/2a

    x = -b/2a + SquareRoot( b2 - 4ac)/2a

    The above is close enough to the standard formula.
    Live long & prosper.

    The Dinosaur from prehistoric era prior to computers.

    Eschew obfuscation!
    If a billion people believe a foolish idea, it is still a foolish idea!
    VB.net 2010 Express
    64Bit & 32Bit Windows 7 & Windows XP. I run 4 operating systems on a single PC.
    Reply With Quote Reply With Quote
  6. Sep 6th, 2003, 05:15 PM #5
    nishantp
    nishantp is offline
    Frenzied Member nishantp's Avatar
    Join Date
    Jan 2001
    Location
    Where you least expect me to be
    Posts
    1,375
    You may want to mention that the b2/4a2 comes from completing the square.
    You just proved that sig advertisements work.
    Reply With Quote Reply With Quote
« Previous Thread | Next Thread »

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Forum Rules


Click Here to Expand Forum to Full Width