Question 4.1.5: Finding Coterminal Angles Assume the following angles are in...
Finding Coterminal Angles
Assume the following angles are in standard position. Find a positive angle less than 360° that is coterminal with each of the following:
a. a 420° angle b. a – 120° angle.
We obtain the coterminal angle by adding or subtracting 360°. The requirement to obtain a positive angle less than 360° determines whether we should add or subtract.
a. For a 420° angle, subtract 360° to find a positive coterminal angle.
420° – 360° = 60°
A 60° angle is coterminal with a 420° angle. Figure 4.16(a) illustrates that these angles have the same initial and terminal sides.
b. For a -120° angle, add 360° to find a positive coterminal angle.
–120° + 360° = 240°
A 240° angle is coterminal with a – 120°. Figure 4.16(b) illustrates that these angles have the same initial and terminal sides.
