Why we need an angle to for trig ratios?

Question

Like f(x)=2x+3 is a function. If we input the value of x so it will apply operations on the value of x and give back a result but in trig function i.e. Sin (X)= opp/hyp But it doesn't apply operations on the input. So my question is why we need an input for that?

Answer 1

But it doesn't apply operations on the input.

Your can better ask "why the input isn't (opp,hyp)"? Or (adj,hyp)...

In a first moment, the input can be considered the triangle.

Then we see that similar triangles give the same answer.

What common data have similar triangles?

The angles.

$\sin$ and $\cos$ depend of the angle between the adjacent side and the hypothenuse.