http://b.scorecardresearch.com/b?c1=...6=&cv=1.3&cj=1

I need some help on how to prove this statement. I don't know where to start!

Prove that if d and n are positive integers such that d|n, then φ(dn) = dφ(n).

A lot of help is appreciated.. I tried writing

http://www.mathhelpforum.com/math-he...ff701eea-1.gif and http://www.mathhelpforum.com/math-he...c3f2334f-1.gif where http://www.mathhelpforum.com/math-he...d902a249-1.gif through http://www.mathhelpforum.com/math-he...f1322214-1.gif are the same for both http://www.mathhelpforum.com/math-he...16e091ad-1.gif and http://www.mathhelpforum.com/math-he...b31363a1-1.gif.

But I don't know where to go from there....

Thanks