Let f(x)={ ax, x≤1 } .Find all possible values of a and b
bx² +x +1, x>1 such that f(x) is differentiable at x=1.
Show proper justification.

a. a can be any real number, and b must be 0.
b. a must be 0, and b can be any real number.
c. a must be 1, and b can be any real number.
d. a can be any real number, and b must be 1.