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**calc_help123** Hey i was having a problem with a hw problem

the function f(x)=(cosx)^2 +2cosx over one complete period begining with x=0

First we have to fun all values of x in this period when f(x)=0.

I know the period is 0-2π by looking at the graph however I dont know how to firgure it out analyitically though. So i found the zeroes but again i dont know how to do it analytically bc i am not got with sins and cos

Second we have to find all values of x in the period at which the function has a minimum.

3rd we have to find when the period is concave up but i dont know how to find the 2nd derivative of a cos