Use the Pythagorean Theorem, what is the length of the hypotenuse in a right triangle whose legs are 3 and 4?

1 Answer
Aug 3, 2016

5 units. This is a very famous triangle.

Explanation:

If a,ba,b are the lehs of a right triangle and cc is the hypoteneuse, then the Pythagorean Theorem gives:

c^2=a^2+b^2c2=a2+b2

Then since the side lengths are positive:

c=\sqrt{a^2+b^2}c=a2+b2

Put in a=3, b=4a=3,b=4:

c=\sqrt{3^2+4^2}c=32+42
=\sqrt{25}=5=25=5.

The fact that a triangle with sides of 3, 4, and 5 units is a right triangle has been known since at keast the ancient Egyptians. This is the Egyptian triangle, believed to be used by the ancient Egyptians to construct right angles -- for example, in the Pyramids (https://nrich.maths.org/982).