Quandaries
and Queries 

I have a question on the
tangent to a quadratic curve. My question is, how is the point d of this tangent determined? It is the point on the yaxis where the tangent cuts isn't it? Is there a formula for it? 

Hi, I drew a diagram of what you described with one change in notation. Since you are using x as the independent variable to describe an arbitrary point on the parabola I used p as the first coordinate of the specific point on the parabola where you have constructed the tangent. I called the second coordinate of this point q.
Since the point (p,q) is on the parabola you can find q,
The point (p,q) is also on the tangent line so the coordinates p and q satisfy the equation of the line. Thus
and hence
Penny 

