  The Symmetries of Feynman Integrals method (SFI) associates a natural Lie
group with any diagram, depending only on its topology. The group acts on
parameter space and the method determines the integral's dependence within
group orbits. This paper analyzes the bubble diagram, namely the 1-loop
propagator diagram, through the SFI method. This is the first diagram with
external legs to be analyzed within SFI, and the method is generalized to
include this case. The set of differential equation is obtained. In order to
solve it the set is transformed into partially invariants variables. The
equations are integrated to reproduce the integral's value. This value is
interpreted in terms of triangle geometry suggested by extant papers.
