In Try This 1 you found patterns for coterminal angles. Since you can keep rotating the terminal arm counterclockwise or clockwise, there is an infinite number of coterminal angles. This means you can keep adding or subtracting multiples of 360° or 2π. You can use both of the following expressions to describe all possible coterminal angles.
θ ± (360°)n or θ ± 2πn, n ∈ N 
θ + (360°)n or θ + 2πn, n ∈ I
Read “Example 3” on page 172 in the textbook. Notice the following as you read:
- All angles coterminal with a given angle can be expressed using the general form.
- When using the general form, it is important to explain what n represents by using n ∈ N. Otherwise, n is assumed to be all real numbers, which would then produce angles that are not coterminal with the original angle.
Self-Check 2
Complete questions 9.a., 9.b., 9.c., 11.a., 11.b., and 11.d. on page 176 of the textbook. Answer
