A: 1. We often use that the sum of two sides in geometry is greater than the third side: choosing the shortest route is to go straight without turning.

2. Always build houses with rectangular floor plan, draw lines and measure land with Pythagorean theorem.

3. When installing the door, check whether the door is on a plane. If it is not on the same plane, the door will tilt up and not lock up and down; Also check whether the diagonal lines are equal. If they are not equal, the door will not close and be stuck by the door frame or the ground.

4, the construction of large buildings, materials, labor should use mathematical calculation.

5, commodity exchange must use mathematics to do value evaluation.

6. Mathematics should be used to determine the number of soldiers used in combat, prepare food and grass, and the time needed to get to a place, and draw a battle map.

In short, in ancient life, mathematical knowledge was everywhere. The list goes on and on.