geometry
The impossible becomes possible when you move into the third dimension. 

How calculating the height of a frustum gave a glimpse of the mathematical frontier. 

The division of plant cells is governed by their shape – just one example of how maths may reveal the fundamental laws underlying biology. 

How to derive the famous quadratic formula from pictures, just like the Babylonians did. 
Euclid's fourth axiom says that all right angles are equal. But isn't that obvious? 