I don't understand what to do here i know it isnt hard kind of confusing me and clue?? I am using matlab

The Taylor series expansion for cos(x is: cos(x) = where z is in radians. Write a MATLAB program that determines cos( using the Taylor series expansion. The program should use a loop for adding terms. If an is the nth term in the series, then the sum Sn of the n terms is Sn-Sn-a. The program should terminate when the estimated error TL n-1 Sn-1 is S.000001