Two or more angles are coterminal if they have the same terminal side position. Any coterminal angle can be represented by the expression θ + n(360), where θ is the reference angle and n is an integer. The reference angle is the acute angle formed between the terminal side and the x-axis, and is always between 0 and 180 degrees.

1. Angles in
Standard Position

2. P (x,y)
θ
Terminal side
Initial side
A (r,0)

3. What are coterminal angles?

4. Remember!
Two or more angles in standard position are
coterminal angles if the position of P is the same for
each angle.
If θ represents any angle, then any angle coterminal
with θ is represented by this expression, where n is
an integer, θ + n(360).

5. Example 1: θ = 150
A. Draw the angle θ in
standard position.
B. Find an angle which is
coterminal with θ.
C. Write an expression to
represent any angle
coterminal with θ.

6. What is reference angle?
For any angle θ in
standard position, its
reference angle (or related
angle) is the acute angle
formed by the terminal side
of θ and the x-axis.

7. Find the reference angle for each angle:
1. 150
2. -280
3. 472