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Dear Student,
 
In a parallelogram opposite angles are equal therefore,
∠∠ABC = ∠∠ADC 
Now, ∠∠ABC + ∠∠EBC = 180 (Linear Pair angles)
∠∠EBC = 180 - ​ ∠∠ABC ............. (1)
 
Also, ​∠∠ADC + ∠∠CDF = 180 ​(Linear Pair angles)
∠∠CDF = 180 - ​∠∠ADC ............... (2)
From (1) and (2) ,
∠∠EBC = ​∠∠CDF ..............(3) (Since ​∠∠ABC = ∠∠ADC ) 
 
Opposites sides of a parallelogram are equal therefore
AB = DC 
but, AB = BE
hence, DC = BE ............ (4)
 
Similarly, DF = BC ............ (5)
 
In triangle BEC and triangle DCF
 
BE = DC (From (4) )
∠∠EBC = ​∠∠CDF (From (3) )
BC = DF (From (5) )
 
Therefore the two triangles are similar by SAS (Side Angle Side) test
 
Regards

  • 1
Dear Student,

In a parallelogram opposite angles are equal therefore,
∠∠ABC = ∠∠ADC 
Now, ∠∠ABC + ∠∠EBC = 180              (Linear Pair angles)
∠∠EBC = 180 - ​ ∠∠ABC   ............. (1)

Also, ​∠∠ADC + ∠∠CDF = 180              ​(Linear Pair angles)
∠∠CDF = 180 - ​∠∠ADC   ............... (2)
From (1) and (2) ,
∠∠EBC = ​∠∠CDF      ..............(3)       (Since ​∠∠ABC = ∠∠ADC ) 

Opposites sides of a parallelogram are equal therefore
AB = DC 
but, AB = BE
hence, DC = BE        ............ (4)

Similarly, DF = BC  ............ (5)

In triangle BEC and triangle DCF

BE = DC                      (From (4) )
∠∠EBC = ​∠∠CDF          (From (3) )
BC = DF                      (From (5) )

Therefore the two triangles are similar by SAS (Side Angle Side) test

Regards
  • 1

∠BAD=∠CDF (Corresponding angles for parallel lines AB and CD)
∠BAD=∠CBE (Corresponding angles for parallel lines AB and CD)
Thus, ∠CDF=∠CBE (I)
We know, AD=BC (ABCD is a parallelogram)
and AD=DF (Given)
Thus, DF=BC (II)
Similarly, BE=CD (III)
Now, In △CDF and △CBE
∠CDF=∠CBE (From I)
FD=BC (From II) 
BE=CD (From III)
Thus, △FDC≅△CBE (SAS rule)
△BEC≅△DCF

  • 1
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