Euclid
Mathematician
Euclid's Theorem
Euclid has many theorems that he uses. I only chose one of those. The one I chose was one of his Books of Elements. That was using magnitude and ratios. Magnitude and ratios are used to find the length, area, and volume of an object. For example if he wanted to find the length of an object he would use Book of Elements with finding magnitude and ratios. If you don't know what magnitude means, it means a number characteristic of a quantity and forming a basis for comparison with similar quantities, as length.
Using it in the real world
People use this theorem in the real world more than you think. People use this for building stuff. For example, if someone was building a house, they would want to know the length of wood, steel, iron, or whatever they were using. They would want to know that because if you didn't know the length of that object then your house would most likely to fall apart or be lopsided.
Pictures
Videos
Euclid's elements: definitions, postulates, and axioms
Euclid's elements: proposition 1