# Thread: Why is 'a' proportional to 'bc', not 'root bc'?

1. Hey, this is getting on my nerves. I have been thinking over this very fundamental thing of Mathematics for quite a long time without finding any possible solution. Here it goes.

Say, 'a' is proportional to 'b', and 'a' is again proportional to 'c', then we may infer a conclusion from this that 'a' is proportional to 'bc'.

Fine! This is true indeed. Every now and then we use this conclusion in Physics. So what I want now is a mathematical proof of this assertion, which I have been trying to find with no success at all. Please help.

2.

3. Originally Posted by J Rahman
Hey, this is getting on my nerves. I have been thinking over this very fundamental thing of Mathematics for quite a long time without finding any possible solution. Here it goes.

Say, 'a' is proportional to 'b', and 'a' is again proportional to 'c', then we may infer a conclusion from this that 'a' is proportional to 'bc'.

Fine! This is true indeed. Every now and then we use this conclusion in Physics. So what I want now is a mathematical proof of this assertion, which I have been trying to find with no success at all. Please help.
It is wrong.

a is proportional to a
a is still proportional to a

a is NOT proportional to a^2

4. No no, you dint get my point. Let me give you an example. The physicists say, F is proportional to q1q2, and F is proportional to 1/r^2, therefore F is proportional to q1q2/r^2. My question is, how do they make this combination? There are many other similar examples in Physics where they make use of this combination principle. I want the mathematical proof -- how do they derive the "conclusion" from the "given".

5. Originally Posted by J Rahman
No no, you dint get my point. Let me give you an example. The physicists say, F is proportional to q1q2, and F is proportional to 1/r^2, therefore F is proportional to q1q2/r^2. My question is, how do they make this combination? There are many other similar examples in Physics where they make use of this combination principle. I want the mathematical proof -- how do they derive the "conclusion" from the "given".
It is still wrong, for exactly the reason that I gave you.

You are the one not getting the point.

If F is proportional to q1q2 and proportional to 1/r*2 then even if F =constant x q1q2/r^2 it is proportional to q1q2 for r fixed or to 1/r^2 for q1q2 fixed but it is only proportional to q1q2/r^2 if that ratio is fixed.

6. Thank you sir. Thank you very much. I am such a brainless moron. It was obvious. I am clear now. Thank you once again.

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