can a reference angle be negative?
Tye "reference angle" in google and check out the mathwords site :)
I copied and pasted the mathwords page for you, unfortunatly the diagram that was with it cant, express itself in text so it didn't appear.
For any given angle, its reference angle is an acute version of that angle. In standard position, the reference angle is the smallest angle between the terminal side and the x-axis. The values of the trig functions of angle θ are the same as the trig values of the reference angle for θ, give or take a minus sign.