# Math Help - the Euler φ-function

1. ## the Euler φ-function

Let x and y be integers; gcd(x,y)=g

Prove that,

φ(xy) = φ(x)φ(y)g/φ(g).

2. Originally Posted by swallenberg
Let x and y be integers; gcd(x,y)=g

Prove that,

φ(xy) = φ(x)φ(y)g/φ(g).

try to use the fact that if gdc(m,n) = 1 then φ(mn) = φ(m)φ(n) and
φ(n) = product of (1-1/pi), where pi is a prime that divides n.

I think this should help...