Kappa curve

Isaac Barrow used this quartic as an early example of finding a tangent by rudimentary calculus, after Gérard van Gutschoven had studied it around 1662. It is named for the Greek letter kappa, though mathcurve finds it looks more like an x. Each line through O meets the line x = a at a point N, and the curve’s point on that line lies as far from O as N lies from A(a, 0).

x²(x² + y²) = a²y²

On mathcurve.com as Kappa