A quantity which is increased or decreased by an infinitely small quantity is neither increased nor decreased.

A quantity which is increased or decreased by an infinitely small quantity is neither increased nor decreased.

But just as much as it is easy to find the differential [derivative] of a given quantity, so it is difficult to find the integral of a given differential. Moreover, sometimes we cannot say with certainty whether the integral of a given quantity can be found or not.

The solution "cost me study that robbed me of rest for an entire night."