Exercise 1 Let A and B be two natural numbers. Follow the proof given below and identify which step(s) is (are) not valid. Step# Equation Justification A=B Assumption Multiply by B on each side Subtract B on each side Factorize Simplify: divide by A-B Base on step 1, A = B, therefore A + B = B + B By definition, BB-2B Simplify: divide by B (A-B)(A + B) = (A-B)13 A+B=B 2B = B 8 There is only one mistake in the proof, in step 5: we cannot divide by A-B as A = B. i.e