The theorem of Torricelli allows the definite integrals calculus, avoiding the calculus of  limit of series, searching for a primitive of the given function. If g(x) is any primitive function of f(x) it has the form:
	x
g(x)=	òf(t)dt+k    Putting x = a  we obtain:
	a
	a		a
g(a)=	òf(t)dt+k    that is to say  k=g(a)     (since		òf(t)dt=0)
	a	x	a
Replacing g(a)  to k::  g(x)=		òf(t)dt+g(a)
		a
		x
from which, inversely:		òf(t)dt=g(x)-g(a)
		a
		b
Finally, replacing b value to x:		òf(t)dt=g(b)-g(a)
		a