Question

What is the domain of y = cos θ

Answer 1

All real numbers / all x 
if you're asking for range as well then its -1<x<1

Answer 2

Answer:

The domain is all real numbers or $x\in(-\infty,\infty)$

Step-by-step explanation:

The definition of domain is :

Domain is the set of x values for which the function is defined.

The given function is y = cos θ and we know that θ can take any value. In other words, for any value of θ, the function  y = cos θ is defined.

Therefore, we can conclude that the domain of y = cos θ is the set of all real values.

In interval notation we can write it as

$x\in(-\infty,\infty)$