The intent of the construction appears to be to produce tangents from point P to the circle O. There are several possible next steps:
• Name the point of intersection just created between the arc and circle O
• Draw a line (or segment) between points P and J
• Draw a line (or segment) between point P and the intersecting point just created on circle O.

The Jacobian has determinant
This isn't necessarily true. When two lines have equivalent slopes, then they are parallel and will never intersect.
y=1/2x + 12
y=1/2x + -2
These lines can't intersect because there are equal slopes.
Cos A cos B + sin A sin B