If domain and range of a function is plot on a axis plane,
x axis will be domain and y axis will be range.
In most of cases in trignometric function, the angle (θ) will be the domain. And what we have to found is the range. Thats why we say domain is the input and range is the output
Eg:-
find domain and range if sinθ ?
Domain - is the angle that changes from 0° to 360°.
Range - is the output. That is sinθ.
sinθ changes from -1 to 1.