Past exam of the mathematics course of the University of Cambridge 2025 iii Paper 166 3 b Solution Created 2026-09-24 Updated 2026-09-24
Writeso there are unknown integer coefficients. Let be the number of integers withFor each such , impose the linear equation over where is the normalized derivative of a polynomial. The coefficient of is and that of is . The local definition of projective height, together with , givesfor a constant depending only on .
There are forms over the degree- field , andMoreover . Applying Siegel lemma gives a nonzero integral coefficient vector withbecause the exponent is bounded in terms of and every fixed power of is at most exponential in . These have all the required vanishing normalized derivatives.
Past exam of the mathematics course of the University of Cambridge 2025 iii Paper 166 3 e Solution Created 2026-09-24 Updated 2026-09-24
It is enough to prove the result for , since a construction for a smaller positive value gives the weaker vanishing requirement for any larger one. Apply part (b) with . For large , part (c) gives linearly independent polynomials , andsatisfies and has order at leastat after setting .
Set . By the rational multiplicity bound for a linear auxiliary polynomial, once is sufficiently large, the one-variable polynomial has multiplicity at most at . Consequently there is some integer such thatPut . The normalized derivative of a polynomial preserves integral coefficients and multiplies height by at most , so . Differentiation lowers the vanishing order at by at most ; for sufficiently large ,Finally write by replacing the coefficient of by its negative. Then and all the claimed bounds hold.