Thales & Pythagoras: Early Contributions to Geometry

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  • 0:05 Geometry
  • 0:49 Thales
  • 2:19 Pythagoras
  • 3:36 Today
  • 4:06 Lesson Summary
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Lesson Transcript
Instructor: Yuanxin (Amy) Yang Alcocer

Amy has a master's degree in secondary education and has taught math at a public charter high school.

In this video lesson, you will learn about the contributions Thales and Pythagoras made to the study of geometry. Also learn which of their major contributions is still in use today.


Geometry is about shapes. It is about defining the characteristics of different shapes. It is about drawing shapes and being able to calculate their dimensions, areas, and volumes. Today, we have formulas that have been proven to work time and time again over the centuries. We have systems in place that help us to visualize and work out problems. But how did they come about? It is all thanks to people like Thales and Pythagoras that we are where we are today in the field of geometry. This video lesson is all about the contributions Thales and Pythagoras made to the study of geometry. Watch and see which one of their teachings you use the most.


Thales comes from Miletus in Asia Minor and was a Greek. He was born around 624 BC and died around 547 BC. Yes, that was a long time ago, but he made some very major contributions to the field of geometry. In fact, some consider him the first mathematician. On a visit to Egypt, he was able to calculate the height of a pyramid. He is credited for making five notable contributions to the field of geometry, one of which is named after him.

The first is that the diameter of a circle bisects, or cuts, the circle in half. The second is that the base angles of an isosceles triangle are equal to each other. The third is when you have two straight lines intersecting each other, the opposite or vertical angles are equal to each other. The fourth notable contribution states that when two triangles have two equal angles and one equal side, then they are congruent, or equal, to each other. The fifth is called Thales' Theorem. It states that an angle that is inscribed or drawn inside a half-circle or semicircle will be a right angle. These five contributions are credited to Thales because he provided the first written proof of these theorems. Now, let's talk about Pythagoras.


Pythagoras was born around 569 BC in Greece and lived to sometime around 500 - 475 BC. While Thales was referred to as the first mathematician, Pythagoras was called the first pure mathematician. No wonder, since Thales had actually given Pythagoras advice on how he could advance his mathematical knowledge. Pythagoras also made major contributions to the study of geometry and he is given credit for the following four teachings.

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