For a real parameter k, define the function gk:[0,2π]→R by gk(x)=ksinx−cosx.
a. (i) Compute gk′(x).
b. (ii) Determine all real values of k for which gk is increasing on the entire interval [0,2π].
c. (iii) For the least value of k obtained in (ii), evaluate gk(0).