Show that cos(2x) -1/cosx - 1 = 4 . Do this by first creating a vector x

Question:

Show that cos(2x) -1/cosx - 1 = 4 .
Do this by first creating a vector x that has the elements 1.0, 0.5, 0.1, 0.01, 0.001, and 0.0001. Then, create a new vector y in which each element is determined from the elements of x by cos(2x) – 1/cosx – 1. Compare the elements of y with the value 4 (use format long to display the numbers).