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Spirals

Hyperbolic spiral

r = a/θ: it winds in towards the pole forever while its far end runs along the line y = a.

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Formulas and key values

Polar equation
r=aθr = \frac{a}{\theta}
Asymptote
y=ay = a

a sets the scale (a = 1 in the graph) and is also the height of the asymptote.

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01 · Definition

What is the Hyperbolic spiral?

Pierre Varignon studied the hyperbolic spiral in 1704. Its equation r = a/θ is the Archimedean spiral turned inside out: the radius shrinks in proportion to 1/θ, so the curve circles the pole infinitely many times without ever reaching it.

At the other end something unexpected happens. As θ goes to 0 the radius grows without bound, but the height r·sin θ = a·sin θ/θ tends to a, so the curve settles onto the horizontal asymptote y = a.

02 · Properties

Key properties

  1. Horizontal asymptote y = a as θ → 0.
  2. Winds around the pole infinitely often as θ → ∞, never reaching it.
  3. Inversion in the unit circle maps it to the Archimedean spiral r = θ/a.
  4. Each turn shrinks the radius by a factor θ/(θ + 2π), not a constant ratio.
  5. Studied by Pierre Varignon in 1704.

03 · Questions

Hyperbolic spiral: common questions

What is the equation of the Hyperbolic spiral?
Polar equation: r = a/θ. a sets the scale (a = 1 in the graph) and is also the height of the asymptote.

04 · Keep exploring