a)Express 2cosx+ sinx in the form Rcos(x-A)

b) Solve the equation 2cosx+ sinx= 1 giving all solutions between 0 and 360 degrees.

c) Find the exact range of values of the constant K for wich the equation 2cosx+sinx =K has real solutions for x

Id really appreciate it if somone helped me with this question.

I can do part a but not b and c

Thank you.