To find the principal angle when we know that the terminal arm is located in quadrant 2 and has a related acute angle of 55 degrees, we need to consider the definition of the principal angle.
The principal angle is measured from the positive x-axis. In quadrant 2, angles are measured in a counterclockwise direction starting from the positive x-axis. Since the related acute angle given is 55 degrees, we can determine the principal angle by subtracting this acute angle from 180 degrees.
So, we calculate:
Principal Angle = 180 degrees – 55 degrees = 125 degrees.
This means the principal angle corresponding to the terminal arm located in quadrant 2 with a related acute angle of 55 degrees is 125 degrees.