Past exam of the mathematics course of the University of Cambridge 2019 ii Paper 1 25F a i Solution Created 2026-09-24 Updated 2026-10-03
WriteThe equation splits the analysis into two cases. If , the remaining equation is , giving the cuspidal cubicIt is irreducible because is irreducible in : as a quadratic in , it could factor only if were a square in .
If , the other equations becomeTheir solutions are , which already lies on , and the two pointsThus the irreducible components areEquivalently, the radical ideal of the cusp with two isolated-point components is