A student named Elena makes the claim that there is a finite set of prime numbers P={p1,p2,p3,…,pk}P = \{p_1, p_2, p_3, \dots, p_k\}P={p1,p2,p3,…,pk} where pk p_k\,pk is the largest prime. Use the method of proof by contradiction to show that Elena's claim is incorrect, and thus prove that there are infinitely many prime numbers.
107 exam-style questions on OCR A Level Maths 1.1 Proof, covering 1.1.1 Structure of mathematical proof, 1.1.2 Logical connectives, 1.1.3 Disproof by counter example, 1.1.4 Proof by contradiction (A-level only), and 1.1 Proof. Each one has a worked solution and a mark scheme showing where the marks go.