# 7. Lissajous Figures

by M. Bourne

We can obtain very interesting graphs when each of the
*x-* and *y-* coordinates are given as functions of
*t*. In this case, we have **parametric equations.** (We see another example of parametric equations later in the applications of differentiation section.)

**Lissajous Figures** are a special case of parametric equations, where *x* and *y* are in the following form:

`x = A\ sin(at + δ)`

`y = B\ sin(bt + γ)`

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[These can also be written in terms of cosine expressions, or a combination of sin and cos, since we can shift sine onto cosine easily. See Graphs of y = a sin(bx + c).]

Lissajous curves can be seen on **oscilloscopes** and are the
result of combining 2 trigonometric curves at right angles.

### Example 1

### Need Graph Paper?

Sketch the graph of the parametric equation where:

x= 2 cost

y= cos(t+ 4)

## Common Lissajous Curves

Lissajous curves take certain common shapes depending on the values of the variables in the expressions

x=Asin(at+δ) and

y=Bsin(bt+γ)

In Example 1, we saw that the curve was an ellipse. If *A* ≠ *B* and *a *=* b*, we obtain an ellipse. (See more on the Ellipse.)

In the example in Curvilinear Motion, the Lissajous figure is a circle. If *A *=* B* and *a *=* b *= 1, we will get a circle.

Example 3 on this page is part of a parabola. We can also obtain a straight line as well.

### Example 2 - ABC Logo

The Australian Broadcasting Corporation is a (mostly!) high quality public television and radio network. The ABC logo is a Lissajous figure. The parametric equations that describe the logo are:

x= sint

y= cos 3t

The graph is as follows:

ABC logo

*x* = sin(*t*),

*y* = cos(3*t*)

For more information by the ABC, see The ABC's of Lissajous Figures.

### Example 3

Sketch the graph of the parametric function:

`x = cos(t + π/4)`

`y = sin\ 2t`

### Example 4 - Mathematical heart

This last one's not actually a Lissajous figure, but like such curves, it's made of parametric equations involving trigonometric functions.

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