Solve a Dilemma

    What is wrong with this proof?

2= 1

a= b

a² = ab

a² -b² = ab -b²

(a +b) (a -b) = b (a-b)

a+ b  =b

2b = b

2 = 1                                                                                                                                                                                    

Answer:   since a = b, a – b = 0. Hence division by zero.