In the design of a custom optical lens, the focal length FFF is calculated as the arithmetic mean of a rational base length LLL and an irrational correction factor γ\gammaγ.
Given that F=L+γ2F = \frac{L + \gamma}{2}F=2L+γ, prove by contradiction that the focal length FFF must be an irrational number.
368 exam-style questions on Edexcel A Level Maths Algebraic Methods, covering 1.1 Proof by Contradiction, 1.2 Algebraic Fractions, 1.3 Partial Fractions, 1.4 Repeated Factors, and 1.5 Algebraic Division. Each one has a worked solution and a mark scheme showing where the marks go.