Answer:
Option d.
±π/2 ; ±3π/2
Explanation:
To quickly solve this problem, we can use a graphing tool or a calculator to plot the equation.
Please see the attached image below, to find more information about the graph
The equation is:
f(x)= 3*cos (x)
We can see from the graph that the zeros are
±π/2 ; ±3π/2
Correct option is d.