It could be written as
\sqrt{sin^{2}x+cos^{2}x-2sinx cosx}
which is
|sinx-cosx|
now 2 cases arise
when sinx >cosx(∩/4,∩/2)................sinx -cosx
and cos x >sinx (0,∩/4)....................cosx-sinx
so f'(x) is cosx+sinx(∩/4,∩/2)
and -(sinx+cosx)(0,∩/4)
so answer is a and b
if its not matching then the answer given must ewrong