Explaination why `cos(0)=1`

requires to refer to the function definition.

`cos(α)`

has been defined as:

Lets suppose that: __alpha angle__ goes to zero (`α -> 0`

) and __adjacent side__ is constant (`b = const`

).

It causes: __opposite side__ goes to zero too (`a -> 0`

) and __hypotenuse side__ goes to __adjacent side__ (`h -> b`

). When angle is equal to `0`

and `b`

is equal to `h`

then `b`

divided by `h`

is equal to `1`

. It means `cos(0)`

is equal to `1`

acording to above definition.

Simple visualisation is presented on below picture: