Hi Kai!
Think you're missing an equal sign. Cosθ = 4/5, Tanθ < 0
The only quadrants where Cosθ is + is I and IV. Since
Tanθ < 0, this must place the angle in the 4th quadrant.
Will call the reference angle θ ', where θ ' = 360 - θ
4
-
5
------------------------
\ θ ' |
\ | -3
1 \ | --
\ | 5
Sinθ = opp/hyp = (-3/5) / 1 = -3/5
Tanθ = opp/adj = (-3/5) / (4/5) = -3/4
Cscθ = hyp/opp = 1/(-3/5) = -5/3
Secθ = hyp/adj = 1/(4/5) = 5/4
Cotθ = adj/opp = (4/5)/(-3/5) = -4/3