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.
107 exam-style questions on Edexcel A Level Maths 1.1 Proof by Contradiction. Each one has a worked solution and a mark scheme showing where the marks go.