cot(90° + a) = -tana

cot(90° - a) = tana

cot(180° + a) = cota

cot(180° - a) = -cota

cot(270° + a) = -tana

cot(270° - a) = tana

cot(360° + a) = cota

cot(360° - a) = -cota