释义 |
Ellipse EnvelopeConsider the family of Ellipses
 | (1) |
for . The Partial Derivative with respect to is
 | (2) |
 | (3) |
Combining (1) and (3) gives the set of equations
 | (4) |
where the Discriminant is
 | (6) |
so (5) becomes
 | (7) |
Eliminating then gives
 | (8) |
which is the equation of the Astroid.If the curve is instead represented parametrically, then
Solving | |  | (11) | for gives
 | (12) |
so substituting this back into (9) and (10) gives
the parametric equations of the Astroid.See also Astroid, Ellipse, Envelope |