The supplement of an angle will be its difference from 180° (or -180°). Hence your supplements are .. -37° ⇒ -143° or 217° .. -9° ⇒ -171° or 189° .. -84° ⇒ -96° or 264°
Since you allow angles to be negative, I'd probably choose the negative value as the supplement.
_____ If you're going to define angles in such a way as to allow their measures to be negative, then you need to make a corresponding definition of complement and supplement. One definition I've seen of "supplement" is that it meets the requirements that .. sin(θ) = sin(supplement(θ)) .. cos(θ) = -cos(supplement(θ))
The above angles (either positive or negative) will meet these requirements.
