How it works
Fifty-one pictures to plot on polar graph paper, each with the equations that draw it: flowers from rose curves, hearts and shells from cardioids and limaçons, spirals, butterflies and bows. Every equation was plotted before it was listed.
Read the full guide
Change the numbers
Many hints say what one number in the equation does. In a rose curve such as r = 4 cos(3θ), an odd number beside θ gives that many petals and an even number twice as many. In a limaçon such as r = 3 + 2 cos θ, the two numbers decide between a dimple, a point and an inner loop.
From one equation to a whole scene
Level, under More filters, sorts by how many equations a picture needs. A butterfly from one long equation is a single curve; a spider at the hub of a spiral web takes spokes, a spiral, a circle and a rose. The list gives equations, not a printable sheet.
- The spirals use θ in radians: at θ = 2π the coiled rope has gone around once.
Questions and answers
What can you draw with polar equations?
Flowers, hearts, shells, spirals, butterflies and bows. A rose curve draws petals, a cardioid draws a heart or an apple, a limaçon draws a bean or a loop inside a loop, and a lemniscate draws a bow tie.
How many petals does a rose curve have?
For r = a cos(kθ) with k a whole number, k petals when k is odd and 2k petals when k is even. So r = 4 cos(3θ) has three petals and r = 4 cos(2θ) has four.
What polar equation makes a heart?
The cardioid r = 3 - 3 sin θ: a heart with one dent at the top and a round base. The curve is named for its heart-like shape but is as close to an apple, so the list also plots it with a leaf.
What is the equation of the butterfly curve?
r = e^(sin θ) - 2 cos(4θ) + sin^5((2θ - π)/24), with θ running from 0 to 24π. It dates from 1989. The last term is there for looks: it shifts each lap a little, so the wings come out in layers.