- #1
dismo
- 5
- 0
Working in a Hilbert plane, show that any rigid motion that fixes at least three noncollinear points must be the identity.
I am certain that I can claim that:
(i) any translation of the plane will fix none of the points
(ii) any rotation will fix a single point
(iii) any reflection will fix only the points on the line about which the plane is reflected
The trouble is I don't know how to prove that no composition of these could fix only three points in the plane...
Where do I go next?
I am certain that I can claim that:
(i) any translation of the plane will fix none of the points
(ii) any rotation will fix a single point
(iii) any reflection will fix only the points on the line about which the plane is reflected
The trouble is I don't know how to prove that no composition of these could fix only three points in the plane...
Where do I go next?