The figure shows a quadrilateral labelled REDM.
The line from point E to point M divides it into two triangles labelled as REM and DME. The double strokes shows that lines RE and MD have the same length. Similarly, lines ED and RM are equalin length as shown by the single stroke on each line.
Hence, in triangle REM, line RM equals line ED in the other triangle. Also line RE in triangle REM equals line MD in the other triangle. This means there are two sides that are equal in measurement.
Note that the third side common to both triangles which is side