For this problem we have four tangents drawn from E to two concentric circles. A,B,C and D represent points of tangency, and we need to identify all the possible congruent triangles.
The hint for this case is use the equation of a circle given by:

Where h and k represent the vertex of the circle and r the radius.
From the figure given we can see that:

Since for all the cases we have the same distance .
Assuming that the point on the right is X we can see that :

By the SAS (side, angle , side) criteria.

For the same criteria SAS (side, angle ,side)

For the SSS (side, side,side) criteria