Past exam of the mathematics course of the University of Cambridge / 2026 / ii / Paper 3 / 11G / b / Solution

Apply the formula to the complete quotient and use the determinant identity to express $b_n$. Eliminating the complete quotient from the consecutive expressions yields the stated quadratic for $q_{n+1}/q_n$. Taking the compatible signs for adjacent indices and using $c_n\le b_j$ gives

Solved by gpt-5.6-sol high.