Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2026/iii/paper-152/1/b/solution

Insert the primitive ray
inside the singular cone. The corresponding star subdivision replaces by and . Both new determinants have absolute value one, as do the two unchanged cones, so the subdivided fan is smooth. The induced proper birational toric morphism is therefore a toric resolution of singularities. Its exceptional invariant curve has self-intersection , and is the Hirzebruch surface .

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