The first obvious thing to do is use the identity 

 to simplify.

 becomes



Its average (not instantaneous!) rate of change over 

is  



which simplifies to



Then we use the identity: 

I won't go through the details, but that simplifies to

}
Now you finish by solving this equality:



to find some zeros which will be answers to c) and which
will also be critical numbers for a) and b).  Then solve this



for a)

and this



for (b)

Edwin