From: Rimantas Liubertas <rimantas@...>
Date: 2008-02-28T12:25:26+09:00
Subject: Re: Math problem

<...>
>  And then I much prefer the algebraic solution I worked out in a few
>  seconds on paper when the question was first posed.
<...>

Father: x
Daugher: y
4y - x  = 0
(x + 6) / (y+6) = 3   ->   3y + 18 = x + 6   ->   3y - x = -12

Coefficients:
4, -1
3, -1
Constants
0
-12

>> require 'matrix'
=> true
>> require 'rational'
=> true
>> k = Matrix[*[[4, -1], [-3, 1]].map{|r| r.map{|x| Rational(x)}}].inverse
=> Matrix[[Rational(1, 1), Rational(1, 1)], [Rational(3, 1), Rational(4, 1)]]
>> c = Matrix[[Rational(0)],[Rational(12)]]
=> Matrix[[Rational(0, 1)], [Rational(12, 1)]]
>> (k * c).to_a.flatten.map{|e| e.to_i}
=> [12, 48]


Regards,
Rimantas
--
http://rimantas.com/