Let f(x)=cosx.
(i) Draw the graph of f(x) for the interval −2π≤x≤0, clearly indicating intercepts and extreme points.
(ii) From the graph obtained, determine how many solutions the equation cosx=−21 possesses in −2π≤x≤0, and list all such solutions.
(iii) Using the periodic nature of the cosine function, write the general solution of cosx=−21 for all real x.