Rearranging VariablesDate: 10/01/98 at 18:57:29 From: Pacey Barron Subject: Using variables Dear Dr. Math, How come when you use a variable in a problem sometimes the answer still has a variable, and you can not get an actual number answer? Date: 10/02/98 at 11:39:15 From: Doctor Peterson Subject: Re: Using variables Hi, Pacey. I assume you are not talking about making a mistake in solving the problem. If there is only one variable in the original equation, then either you can solve it with a numerical answer, or you simply can't solve it - there would be no actual solution that still involved the variable. But if you are given an equation with two variables in it, like C = 2*pi*r, and are told to solve it for one of the variables, say r = C/(2*pi), then the other variable will still be there. In this case, you are simply rearranging a formula for a different use. As given, the formula lets you get the circumference of a circle given its radius. After you solve it for r, it lets you find the radius of a circle given its circumference. You don't know either one yet, but if I gave you a circumference, you could plug it right into this formula. If you hadn't already solved for r, you would have to put my value into the original equation for C and then solve that for r. So there are two ways a variable can be used. Sometimes it is an unknown, which you want to figure out from the equation. Other times it just stands for a value that you don't know now, but will know later, like C in my example. Then you just work with it as if it were a value, but without being able to do the calculations. When you're done, you can replace it with any value. - Doctor Peterson, The Math Forum http://mathforum.org/dr.math/ |
Search the Dr. Math Library: |
[Privacy Policy] [Terms of Use]
Ask Dr. Math^{TM}
© 1994- The Math Forum at NCTM. All rights reserved.
http://mathforum.org/dr.math/