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Forum index » Science and Technology » Physics
Quadratic equavasion
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Sergey
science forum beginner


Joined: 19 Jul 2006
Posts: 2

PostPosted: Wed Jul 19, 2006 7:10 pm    Post subject: Quadratic equavasion Reply with quote
I'm saving mutex into window registry for one of my programs, and I am
encrypting it using a simple quadratic equation. Such as y = x^2+20x, where
x is a value of a character (41 through 90), and y is a number I get which I
will store. Now, I was in college just about 4 or 3 years ago, or something
like that, work and all is turning me into moron. How do I solve for x? So
that I can decrypt this back into the character.

y=x^2+20x

x=?
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tadchem
science forum Guru


Joined: 03 May 2005
Posts: 1348

PostPosted: Wed Jul 19, 2006 10:07 pm    Post subject: Re: Quadratic equavasion Reply with quote
Sergey wrote:
Quote:
I'm saving mutex into window registry for one of my programs, and I am
encrypting it using a simple quadratic equation. Such as y = x^2+20x, where
x is a value of a character (41 through 90), and y is a number I get which I
will store. Now, I was in college just about 4 or 3 years ago, or something
like that, work and all is turning me into moron. How do I solve for x? So
that I can decrypt this back into the character.

y=x^2+20x

x=?

The quadratic formula:

If

0 = a*x^2 + b*x + c

then

x = [ - b +/- SQRT( b^2 - 4 * a * c)] / (2 * a)

(you get 2 answers for the price of one:

x = [ - b + SQRT( b^2 - 4 * a * c)] / (2 * a)

and

x = [ - b - SQRT( b^2 - 4 * a * c)] / (2 * a)


In your case, a = 1, b = 20, c = - y

HTH

Tom Davidson
Richmond, VA
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