Euclid's fourth axiom says that all right angles are equal. But isn't that obvious?

Five basic facts from the father of geometry.

Why game theory is a serious business.

The Indian way of adding fractions makes things easier (with musical explanation).

How to lose a spacecraft in the most embarrassing way possible.

How do you write numbers as string of 0s and 1s?

Of numbers, beauty and bizarre animals.

We are very pleased with our new toy demonstrating the curvature of any smooth function – now you can try it out too!

Are there more irrational numbers than rational numbers, or more rational numbers than irrational numbers? Well, there are infinitely many of both, so the question doesn't make sense. It turns out, however, that the set of rational numbers is infinite in a very different way from the set of irrational numbers.

Not necessarily, when it comes to money.

How to make a hard problem easy by changing the way you look at it.

A triangle has many centres....