Past exam of the mathematics course of the University of Cambridge 2001 iii Paper 20 1 Solution Created 2026-10-03 Updated 2026-10-14
We first give an auxiliary-integral proof, rather than deducing both requested results from a theorem only stated later. The following symmetric Hermite integral obstruction will do both jobs. Supposewhere and are integers, the distinct nonzero algebraic exponents form a Galois-stable set, and their weights are invariant under conjugation. Choose vanishing at those exponents, with , and a positive integer for which every is an algebraic integer. For a large prime number , letAt zero, derivatives below vanish; the derivative of order equals . All higher derivatives at zero are integers divisible by . At each , derivatives below vanish and all higher derivatives belong to in a Galois splitting field . Indeed their coefficients contain , divisible by for , and every is integral for . ConsequentlyGalois invariance makes the sum rational, and integrality makes it an integer. For prime numbers not dividing it is nonzero.
But , so integration along the straight segment to givesMultiply by the weights and use the assumed exponential relation. This expresses as the sum of these integrals. On the finitely many fixed segments, their absolute values are at most for a fixed : all polynomial and exponential factors have fixed bounds, and is linear in . Thus , contradicting its being a nonzero integer. The obstruction is proved.
If were algebraic, an integral polynomial relation would give with . Integer exponents and weights satisfy the obstruction, so is transcendental.
If were algebraic, put and let be its algebraic conjugates. Since , the product vanishes. Expand it and collect equal subset sums. The zero sums contribute a positive integer ; the nonzero sums give a Galois-stable list with positive integral multiplicities. This is precisely the prohibited relation. Hence is transcendental.
The general Lindemann–Weierstrass theorem states that exponentials of distinct algebraic numbers are linearly independent over . Suppose the sine quotient were algebraic, say . The denominator is nonzero: would give a forbidden relation between the exponentials of the distinct algebraic numbers . The quotient identity would giveThe four exponents are distinct under the stated nonzero and non-opposite assumptions, so this also contradicts linear independence. Therefore