Is the function value of an angle always equal to the function value of its reference angle?

No, the function value of an angle is not always equal to the function value of its reference angle. Reference angles are used to simplify the calculation of trigonometric functions in certain quadrants, but their values depend on the specific function and the quadrant in which the original angle lies. For example, the sine of an angle in the second quadrant will be equal to the sine of its reference angle, but the cosine will be negative. Thus, while some function values may be equal, others will differ based on the quadrant.