How to convert between radian & degree?

To convert from radians to degrees, multiply by 180/pi. For example when turning 4pi/9 to degrees 

To convert degrees to radians you need to multiply the degree by π and divide by 180. For example when turning 200 degrees into radians 

Why is the name Pythagorean identity appropriate?

Pythagorean Identity is an appropriate name because its the identity that is associated with Pythagorean theorem. Your trying to find a side of a triangle. The Pythagorean identity is sin^2 + cos^2 =1. The Pythagorean theorem is a^2 + b^2 = c^2

How to find Arc length of a circle?

When finding the arc length of an angle you divide the angle measure by 360. Then you multiply that by 2, pie, and the radius.