If y = arctan(cosx), then dy/dx​

Can someone pls ! pls answer all. no explanation needed..

Can someone me with #s 8, 9, and 11. with just one of the three also works. prove using only trig identities.

An office supply company conducted a survey before marketing a new paper shredder designed for home use. in the survey, 80 % of the people who tried the shredder were satisfied with it. because of this high satisfaction rate, the company decided to market the new shredder. assume that 80 % of all people are satisfied with this shredder. during a certain month, 100 customers bought this shredder. find the probability that of these 100 customers, the number who are satisfied is 69 or fewer.