There are trigonometric ratios of 90 degree plus theta.
There is a relation between all six trigonometrical ratios.
The same rotating line rotates in the same direction and makes an angle of 90.
Again, take a point E on OB such that OC is equal to or greater than OX.We get from the right-angled OCD and OEF.
OD are either positive or negative in diagram 1 and 4 OF and DC are opposite signs.OD and FE are both negative in diagram 2 and 3 OF and DC are opposite signs.