​All trigonometric functions are periodic. What is the period of cos x ?​

Correct option is C

Given:

To find ; the period of cos x

Solution:

The cosine function cos x is periodic, meaning it repeats its values at regular intervals. 

The cosine function  cos x completes one full cycle as x increases from 0 to 2π. Therefore:

​$$\cos(x + 2\pi) = \cos x$$ 

Thus, the period of cosine is 2π.​