Assume a rectangle with a width of 1 and a height of pi. The area of the rectangle is width x height = 1 x pi = pi.

Divide the width of the rectangle by two, and multiply the height of the rectangle by two. The area of the rectangle is width x height = 1/2 x 2pi = pi.

Repeat ad infinitum and one arrives at the case of inifinitesimally small x infinitely large. The result is ... pi.

Then again, were the original rectangle of width 1 and height e, then infinitesimally small x infinitely large would equal e.

However useful, infinity and infinitesimality are concepts, not numbers. You cannot just multiply them and expect to get a defined answer in return.