Try this problem from I.S.I. B.Stat Entrance Objective Problem based on Derivative of Function.
Let f(x)=x[x] where [x] denotes the greatest integer smaller than or equal to x where x is not an integer, what is f'(x)?
But try the problem first...
B.Stat Objective Problem 756
Challenges and Thrills of Pre-College Mathematics by University Press
\(f(x)=x[x]\) where f(x) discontinuous at integer points so non differentiable at those pts
so we find for non-integer points
if x is not an integer then [x] is a constant and not equal to x
x is non integer so here [x] is treated as constant here . Let [x] = a then f(x) =ax => f'(x)= a = [x] . Hence option [x] is correct.