Bullet-nose curve

File:Bullet nose curve.svg

Bullet-nose curve with a = 1 and b = 1

In mathematics, a bullet-nose curve is a unicursal quartic curve with three inflection points, given by the equation

$a^2y^2-b^2x^2=x^2y^2 \,$

The bullet curve has three double points in the real projective plane, at x=0 and y=0, x=0 and z=0, and y=0 and z=0, and is therefore a unicursal (rational) curve of genus zero.

If

$f(z) = \sum_{n=0}^{\infty} {2n \choose n} z^{2n+1} = z+2z^3+6z^5+20z^7+\cdots$

then

$y = f\left(\frac{x}{2a}\right)\pm 2b\$

are the two branches of the bullet curve at the origin.