### 26.17.2 Envelopes

The envelope command draws the envelope of a family of curves.

- envelope takes two arguments:
  - expr, an expression of two variables and one parameter.
  - L, a list of the names of the variables and the parameter. If the variables are x and y, then L only need to be the name of the parameter.
- envelope(expr,L) draws the envelope of the family of curves given by expr=0.

#### Example

envelope(y+x*tan(t)-2*sin(t),t)

or:

envelope(v+u*tan(s)-2*sin(s),[u,v,s])