olymmath

Putnam 2021 B3

  • Session B

Let h(x,y)h(x,y) be a real-valued function that is twice continuously differentiable throughout R2\mathbb{R}^2, and define ρ(x,y)=yhx−xhy.\rho(x,y) = yh_x - xh_y. Prove or disprove: For any positive constants dd and rr with d>rd>r, there is a circle S\mathcal{S} of radius rr whose center is a distance dd away from the origin such that the integral of ρ\rho over the interior of S\mathcal{S} is zero.

Curated text Kedlaya Putnam archive. Quoted with source.

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