What is the correct equation for the function whose graph is shown?

a. y = -5 cos 3x
b. y = -3 cos 5x
c. y = 3 cos 5x
d. y = 5 cos 3x

i know its either b or c. but i'm not sure which one relating to the positive/negative 3.

y= 3 cos 5x would be my best educated guess.

options a,b,c are the right answer.

step-by-step explanation:

a linear parent function is always represented as y = x

if we write this function in the form of y=mx+c

⇒

or  

now if we plot a graph we will find these characteristics:

1) y intercept of the graph is zero so its a straight line passing through origin.

2) as we can see in both the forms of function written, values of x and y may be either positive or negative for the positive slope means points on the graph are either in first quadrant or in third one.

3) it's slope is one.