An Arc of a circle is any portion of the circumference.
An Angle is the difference in direction between two straight lines which meet.
If two diameters divide a circle into four equal parts, these diameters make right angles with each other.
An angle less than a right angle is an acute angle.
The circumference of a circle may be divided into 360 equal parts, called degrees. If the circle is large, the degree is large, and if the circle is small, the degree is small, but the degree is always 1⁄360 part of the circumference, whatever the size of the circle.
An angle at the center of a circle is measured by the arc which bounds it.
If the angle is a right angle, it is measured by 1⁄4 of 360 degrees, or 90 degrees; hence, any angle of 90 degrees is a right angle.
An acute angle is always less than 90 degrees.
An obtuse angle is always more than 90 degrees.
Table of Circular Measure