## Adding and Multiplying with Parallel lines

**Interactive Course on Projective Geometry**

The following geometric constructions using parallel lines construct the
sum and the multiplication of two numbers. They are basically
self-explanatory and you can click on the figures to see a step-by-step
construction or charge the applets to get a better feeling of what's going
on.

*Constructing the sum of two points:*

*Constructing the product of two points:*