Explaining, convincing and proving

Interior angles can help us to work out which polygons will tessellate. Can we use similar ideas to predict which polygons combine to create semi-regular solids?

Can you find the values at the vertices when you know the values on the edges?

Semi-regular tessellations combine two or more different regular polygons to fill the plane. Can you find all the semi-regular tessellations?

Draw some quadrilaterals on a 9-point circle and work out the angles. Is there a theorem?

Can you decide whether these short statistical statements are always, sometimes or never true?

Sequences of multiples keep cropping up...