Leibniz Differential Calculus Example - Manual p. 100

Illustration for page 100 in Math Manual

(a) Where are the lengths Δx and Δy in the diagram? What is happening to each of them as the diagram changes? (b) Are the “assignable” lengths dx and dy in the diagram? Where? What happens to each of them as the diagram changes? (c) Does the ultimate ratio of dy to dx appear in the diagram? Where? Is this a ratio of magnitudes? If so - which ones? If not, what is it?