I’m trying to learn Computational Geometry and this formula isn’t obvious to me.

Hint: "**cross**" is related to the cross product of two vectors .

`// returns intersection of infinite lines ab and pq (undefined if they are parallel) point intersect(c`enter code here`onst point &a, const point &b, const point &p, const point &q) { double d1 = cross(p - a, b - a); double d2 = cross(q - a, b - a); return (d1 * q - d2 * p) / (d1 - d2); } `