# Orthogonal

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*Orthogonal Circles*

Orthogonal circles are orthogonal curves, i.e., they cut one another at right angles. By the Pythagorean theorem, two circles of radii \(r_1\) and \(r_2\) whose centers are a distance \(d\) apart are orthogonal if

\[r_1^2+r_2^2=d^2. \]