For
,
y=sin-1 (sin x)
= sin-1 ( sin (π –(π -x))
(to get y in principal range of sin-1 x)
i.e.,
y = π - x

From the last problem we see that
and 
So, y is not differentiable at 
Extending this, we can say that y is not differentiable at x = (2n+1)
So, for 
(Ans)