The reference angle will be 75 degrees.
What is a reference angle?
The sharp angle is formed by the terminal side or arm and the x-axis. There is always a positive reference angle. The reference angle is, in other words, the angle formed by the terminal side and the x-axis.
The reference angle will be calculated as:-
645 - 360 = 285 It's in the 4th quadrant.
645 - 360 - 360 = -75
Since an angle of 645 deg is coterminal with an angle of -75 degrees, the reference angle is 75 degrees.
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