In a cryptographic protocol, the number of decryption cycles, DDD, required for a security parameter s∈Ns \in \mathbb{N}s∈N is given by D=s2+4s+7D = s^2 + 4s + 7D=s2+4s+7.
Use algebra to prove by contradiction that if D D\,D is even, then s s\,s must be odd.
Practise AQA A Level Maths 1.4 A: Proof with exam-style questions for A Level Maths. 107 questions covering 1.4.1 Structure and methods of proof, matched to the AQA A Level Maths (7357) specification and written in Paper 1, Paper 2 and Paper 3 style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.
