x2+y2=k40,x2+y2=k100x^2 + y^2 = \frac{k}{40}, x^2 + y^2 = \frac{k}{100}x2+y2=40k,x2+y2=100k. Las curvas de nivel representan círculos de radios 10k20\frac{\sqrt{10k}}{20}2010k y k10\frac{\sqrt{k}}{10}10k