How to find 90 degree?

Question

How to find 90 degree?

Answer 1

To make 90 degrees is very simple and practical,

bring a thread of 12 meter or feet, then mark this thread or robe into segments of 3, 4, and 5 stretch the thread by fixing the 4 meter on floor , then change the direction of 3 meters, then join the free end to the start point, therefore the angel between the stretches 3 & 4 makes a 90 degree

Answer 2

Make an L with your thumb perpendicular to your forefinger.  You've found it!

Please, you need to give more information.  Your question is not complete.

Answer 3

The old Pythagorean theorem is a popular tool for constructing a right triangle, usually sides some multiple of 3,4 and 5 units are used. There are various other geometric methods that can be used as well.