Let consider that 1+2+ .. +n = An + Bn + C For all n and for some constant A, B and C. D Assuming that this is true, plug in n= 1, 2, 3 to obtain three equations in the three unknowns A, B and C. 2Solve for A, B and C with the three equations obtained in the previous question. 3 Prove using the mathematical induction that the statement is true.