### Triangle Midpoints

You are only given the three midpoints of the sides of a triangle. How can you construct the original triangle?

### Pareq Exists

Prove that, given any three parallel lines, an equilateral triangle always exists with one vertex on each of the three lines.

### The Medieval Octagon

Medieval stonemasons used a method to construct octagons using ruler and compasses... Is the octagon regular? Proof please.

# Two Points Plus One Line

##### Stage: 4 Challenge Level:
Well done Graham from Feilding High in New Zealand and also to Andrei from Tudor Vianu National College, Bucharest, who both gave good answers to the first part of the problem.

The geometrical solution is to construct the perpendicular bisector of the line $AB$ and mark where it will cross the original line.

This solution works for all cases except where the line $AB$ is itself perpendicular to the original line AND the original line is not the perpendicular bisector of the line $AB$

Can someone now suggest parameters for the general arrangement so that any particular arrangement can be uniquely identified?