If f(x)=x−1−x (Where [X] is greatest integer less than or equal to x) then.

f(1+)=x−1−1=x-2 =1-2 =-1 f1-=-(x-1)-0 =-x+1 =-1+1 =0 Left hand limit is not equal to the right hand limit, so that the function is not differentiable at x=1