I am giving answer for 1 st problem

 

first prove that  tanx+cotx= 2cosec2x  [by converting  sin n cos n taking l.c.m]

                      cotx-tanx=2cot2x

                      substracting  tahe above

   

                    2tanx=2(cosec2x-cot2x)

                   tanx=cosec2x-cot2x

 

put x=15/2

 

and solve for the required answer

 

I think u can do it

 

BYE.........................