Answer:
A pair of intersecting straight lines which agrees with option A of the answers in the list
Step-by-step explanation:
Recall, how a cone is built, as the surface produced by a line (called the "generatrix") as it moves at a fixed angle pivoting around a fixed point that will become the "vertex" of the cone.
As a plane cuts the cone perpendicular to its base and passing through the vertex, it will just intersect the generatrix trajectory in exactly two locations.
a. Practically speaking, you compute the differential in much the same way you compute a derivative via implicit differentiation, but you omit the variable with respect to which you are differentiating.
Aside: Compare this to what happens when you differentiate both sides with respect to some other independent parameter, say :
b. This is just a matter of plugging in and
.