Corina
Grade 9
from Josh (student)

What are some ways that we use the pythagorean theorem in jobs, or even in everyday life?

Hi Josh,

People building fences will use the 3-4-5 triangle to make right angles: Suppose that you have laid the posts on one side

P P P P P P

Where should you lay the next post to continue the fence at a right angle? It is tough to produce a 90 degree angle out in the open with nothing to guide you. One trick is to take a long enough rope and mark off two points A and B on its length such that the lengths of the three segments are proportional to 3, 4, 5:

O---3--A----4---B-----5----O

Have a friend hold the A point on the last fence post, another friend hold both ends together on the line of fence posts already completed, and hold the B point in the direction where you want to continue the fence. Now tighten everything and drive a stake at B.

Since the 3-4-5 triangle is right, you will want to place the new fence line in the direction of the A-B line.