Do any two affine rotations with no common fixed point generate an infinite group?

58 Views Asked by At

Assume we have two affine rotations of the plane around two different fixed points. Do they generate an infinite group?

1

There are 1 best solutions below

3
On BEST ANSWER

If you have a group $G$ of affine self-transformations of a vector space $V$: then if $G$ is finite then $G$ fixes $\frac1{|G|}\sum_{g\in G}g(0)$.

By contraposition, if $G$ is generated by a subset $S$ and there is no common fixed point for elements of $S$, then $G$ is infinite.