how to find lhd and rhd of modulus /absolute function using formula lhd= limit of h approaches to 0 f(c-h)-f(c)/-h ,rhd= limit of h approaches to 0 f(c+h)-f(c)/h ?

if the situation is limit of h approaches to 0 modulus of h-1 + modulus of -h-1+2  whole divided by h  how will  question as such be solved further?

can you explain the whole concept by taking the following question as example using the above formula for lhd and rhd

show that f(x)=modulus of x+1+modulus of x-1 for all x belonging to real numbers r is not differentiable at x=-1 or x=1