In triangle ΔABC and ΔBDE ,
Angle BAC= Angle DBE ,[ BD is parallel to AC ,(alternative angle) ]
Angle ABC = Angle BED = 90 ,(Given)
if two angles of two tringle are equal corresponding then those third angle are also be equal .
so, Angle ABC = Angle BDE
therefore ΔABC is similar to ΔBDE [ By AAA similarity]