Euclid's Elements
Book VII
Proposition 25

If two numbers are relatively prime, then the product of one of them with itself is relatively prime to the remaining one.
Let A and B be two numbers relatively prime, and let A multiplied by itself make C.
java applet or image I say that B and C are relatively prime.

Make D equal to A.

Since A and B are relatively prime, and A equals D, therefore D and B are also relatively prime. Therefore each of the two numbers D and A is relatively prime to B. Therefore the product of D and A is also relatively prime to B. VII.24
But the number which is the product of D and A is C. Therefore C and B are relatively prime.
Therefore, if two numbers are relatively prime, then the product of one of them with itself is relatively prime to the remaining one.
Q.E.D.

Guide

This is a special case of the previous proposition. It is used in VII.27 and IX.15.


Next proposition: VII.26

Previous: VII.24

Book VII introduction

   

© 1996
D.E.Joyce
Clark University