(i) Prove that if a set D has the minimum element then this element is unique in D.

(ii)Give the definition of the differentiability of a function f at a point b

(iii) Investigate whether the function f(x) = 4x3-11x2+14x -17 is differentiable at x = 5.

(iv) For any real number a, give the definition of the absolute value of a.

(v) For any two numbers and b, prove that | | a | -| b | | | a -b |.