Thales used the intercept theorem to measure the height of a pyramid without climbing it. He waited until the sun cast a shadow that was the same length as the pyramid. Then he measured the length of the shadow and his own shadow, and using simple proportion determined the height of the pyramid based on his own height.

1. Intercept theorem
Thales 624-546 BC

2. Thales used a measuring stick and the
sun to measure the height of a
pyramid – how did he do it?