The result of multiplying infinitesimal by infinitesimal is an unknown number. Because infinitesimal is not a definite number. In addition, the order is also different.

Suppose:

A is an infinitesimal number;

b=a*a

c= 1/a

d=2*a

e= 1/(a*a)

So the so-called infinitesimal multiplied by infinity may be:

A*a=b is still infinitesimal;

a*c= 1

A*e= 1/a infinity.

c*d=2