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forum Forum index forumAlgebra forumCramer's rule

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Author : Topic: Cramer's rule  Bottom
 saucer
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 Posts : 673
 A Good Tautology is Hard to Find!
 saucer
  Posted 10/04/2007 12:06:51 AM
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The point of Cramer's Rule is that you don't have to solve the whole system to get the one value you need. This saved me a fair amount of time on some physics tests. I forget what we were working on (something with wires and currents, I think), but Cramer's Rule was so much faster than any other solution method (and God knows I needed the extra time). Don't let all the subscrīpts and stuff confuse you; the Rule is really pretty simple. You just pick the variable you want to solve for, replace that variable's column of values in the coefficient determinant with the answer-column's values, evaluate that determinant, and divide by the coefficient determinant. That's all there is to it.

Almost.

What if the coefficient determinant is zero? You can't divide by zero, so what does this mean? I can't go into the technicalities here, but "D = 0" means that the system of equations has no unique solution. The system may be inconsistent (no solution) or dependent (a parametric solution such as "(a, a + 3, a – 4)"). In terms of Cramer's Rule, "D = 0" means that you'll have to use some other method (such as matrix row operations) to solve the system. If D = 0, you can't use Cramer's Rule .....






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--Last edited by saucer on 2007-08-16 18:10:38 --

 saucer
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 Posts : 673
 A Good Tautology is Hard to Find!
 saucer
  Posted 11/09/2007 00:10:27 AM
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http://www.ee.technion.ac.il/courses/044142/winter03/cramer.gif





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 saucer
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 Posts : 673
 A Good Tautology is Hard to Find!
 saucer
  Posted 29/02/2008 03:05:39 PM
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