Past exam of the mathematics course of the University of Cambridge 2012 iii Paper 27 3 iv Solution Created 2026-10-03 Updated 2026-10-07
We use the canonical height pairing normalization , so that . The supplied values giveThe convention without the factor instead gives the doubled pairing ; all independence conclusions are the same.
In our convention the Gram matrix is approximatelyThis positive margin is much larger than the rounding uncertainty. Even allowing each of the three stated heights an error of , we have , and , giving . Thus the actual canonical height pairing matrix is positive-definite, not merely its rounded approximation.
If for integers , bilinearity and the height parallelogram identity give . Positive definiteness forces . This is the rank certificate from rounded canonical heights, and provesHere the last brackets denote the generated subgroup, not the scalar height pairing. The argument proves independence; it does not assert that these points generate the entire Mordell-Weil group.