What will be the period of trigonometric function cos x ?
A. $ 2\pi $
B. $ 4\pi $
C. $ \dfrac{\pi^2}{4}$
D. None of these

Hint: Let us draw the graph of cos x, because from the graph of any trigonometric function we can directly find its period.

Complete step-by-step answer:
As we know that period means the length from one peak to the next peak or we can say that period is the length from one matching point to another of a period function.
In other words, we can also say that period is the length of one full cycle or the interval of x-values on which the cycle of the graph that’s repeated in both directions lies..
So, as we know that all trigonometric functions are periodic functions.
So, if we are asked to find the period of any function then we have to find the first period of that function.





So, from the above graph we can see that the graph starts repeating after $ 2\pi $.
So, the period of cos x is $ 2\pi $.
Hence, the correct option will be A.

Note: Whenever we come up with this type of problem where we are asked to find the period of any trigonometric function then the easiest and efficient way to find the period is by drawing the graph. We can clearly see that after how much length the graph is repeating. And that will be the period of that function.