Here, RUMH and RUBM are two rhombus as shown in the diagram.
As, a rhombus has four equal sides,
so for RUMH, side RH = side HM = side MU = side UR
and for RUBM, side RM = side MB = side BU = side UR
As HM=UR and MB= UR , so we can write HM = MB
Now for two triangles ΔRHM and ΔUMB,
side RH = side MU
side RM = side BU
and side HM = side MB
'Side Side Side' theorem states that if three sides of one triangle are equal to three sides of another triangle respectively, then the two triangles are similar.
That means, ΔRHM = ΔUMB