Differential calculus

Question

If f(x) = |x-1| + |x-2| is not derivable at x =

(a) x = 0

(b) x = 1,2

(c) x = 3

(d) none

Answer 1

first break the function

now u can see that

f '(2⁺) != f '(2^-)

also  f '(1⁺) != f '(1^-)

so not derivable at x = 1 and 2

Answer 2

X = 0 -> f[x]=3

X= 1 -> f[x]=1

X=2 -> f[x]=1

X=3 -> f[x]=3

So I think it's 1,2 as that's where the tint occurs in graph. Correct me if I am wrong.