they have the same terminal side

the ray on the x-axis

the other ray of the initial side is the angle

a circle is an angle with a vertex at the center of a circle

the portion of the circle w/endpoints on the sides of the central angle

the y coordinate

the x-coordinate

a unit of angle, equal to the center of a circle whose arc is equal in length to the radius

period function half the difference between the max. & min. values

each horizontal translation of certain periodic functions

 a function is the horizontal length of one cycle