Please help me find the equation (:

  y = cos(x)

Step-by-step explanation:

This graph of the cosine function has no shifting or scaling. It is a plain cosine function:

  y = cos(x)

_____

Additional comment

It will be worth your time to learn to recognize the sine and cosine functions. They have a maximum of +1, a minimum of -1 and a period (horizontal distance between corresponding points) of 2π. The sine function is symmetrical about the origin. The cosine function is symmetrical about the y-axis. The maximum slope (near the zero-crossings) is 1.

entering that problem on the tube might get you an answer