How do we prove that the following points are the vertices of an isosceles triangle:- (a,a), (-a,-a) and (-?3a,?3a).

Let A(a,a), B(-a,-a) and C(-a, a)

Now, AB = =

BC = =

=

And, AC =

=

From above, we find that

AB = BC

Thus, the given vertices are of isosceles triangle.