Graph of a quadric : quadrique

### 2.49.7 Graph of a quadric : `quadrique`

`quadrique` takes as arguments the expression of a quadric with respect to x,y,z. You may also specify the variables as a vector (second argument) or as second, third and fourth arguments.
`quadrique` draws this quadric.
Input :

`quadrique(7*x```^```2+4*y```^```2+4*z```^```2+4*x*y- 4*x*z-2*y*z-4*x+5*y+4*z-18)`

Output :

`the drawing of the ellipsoid of equation 7*x```^```2+4*y```^```2+4*z```^```2+4*x*y-4*x*z-2*y*z-4*x+5*y+4*z-18=0`

See also `quadrique_reduite` for the parametric equation of the quadric.