"a telephone line hangs between two poles 14 m apart in the shape of the catenary y = 20cosh(x/20) - 15, where x and y are measured in meters.

(a) find the slope of this curve where it meets the right pole: the slope is sinh(7/20)

(b) find the angle θ between the line and the pole: θ = 90° - α, so my question is, why is there an angle α and where is it located? "