Past exam of the computer science course of the University of Oxford / 2015 / Geometric modelling / 1 / b

Solving the implicit equation for $y$ when $\Delta x\ne 0$ givesHere “gradient” means the slope $dy/dx$, rather than the gradient $(a,b)$ of an implicit defining function. If $\Delta x=0$ and $A\ne B$, the straight line is vertical and has no finite slope. If $\Delta y=0$ and $\Delta x\ne 0$, its slope is zero.