If you have this triangle, whether isosceles or not, then:



The bottom side, that is, the side that connects  and 
can either be called 
        __     __
AB, BA, AB, or BA

The left side, that is, the side that connects  and 
can either be called 
        __     __
AC, CA, AC, or CA

The right side, that is, the side that connects  and 
can either be called 
        __     __
BC, CB, BC, or CB

The angle whose vertex is at point A
can either be called

ÐA, ÐBAC, or ÐCAB

The angle whose vertex is at point B
can either be called

ÐB, ÐABC, or ÐCBA

The angle whose vertex is at point C
can either be called

ÐC, ÐACB, or ÐBCA.

Notice that if you indicate an angle by three letters
the middle letter must be the vertex of the angle indicated,
the letter on the laft must be on one side of the angle
and the letter on the right must be on the other side of the
angle.

If the triangle happens to be isosceles, then two of the sides
are congruent and have the same measure, and the angles whose
vertices are at the points not in common to the congruent sides
are also congruent.

Edwin