Write a script to plot this function in python 2712 - it

Question

Write a script to plot this function in python 2.7.12?

f(j) = ∑_i=0^m-1a_icos(2Πi*j/m) where m is 3? In the case where a₀=a₁=a₂=1, the function looks like this:

Able to input different values of a_i to see how it changes the waveform. It should still look like that if choose a_i values to be 1 after the script.