cos(arccsc(-20))

Im not allowed to have a decimal answer

sinTheta=1/20 in the third or fourth quadrant (sin is negative). so if Sintheta=1/20, the third side must be sqrt399.

so cosine must be sqrt399/20, in the third quadrant , it is negative, in the fourth quadrant it is positive. Take your choice, both are right.

check my thinking.