# General quadrics

## A general quadric has equation

## Ax2 + By2 + Cz2 + Dxy + Eyz + Fxz + Gx + Hy +Iz + J =0

## Intersections with general quadrics are computed in a way similar to cones and cylinders: for a ray p+ v t, take x = px + vx t, y = py + vy t, y = pz + vzt,

## and solve the equation for t; if there are solutions,

## take the smaller nonnegative one.

## Infinite cones and cylinders are special cases of general quadrics.