Answers

2016-03-07T17:09:58+05:30
Angle DAC = Angle BAC
Angle DAC = Angle BAC
But, Angle DAC = Angle BCA (Alternate angles)
Therefore , Angle DCA = Angle CAB = Angle DAC = Angle BCA
Therefore, AB=BC=DC=DA (Sides opposite to equal angles are equal)

Since all sides are equal ABCD is a rhombus.
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Phew! I had to write it two times to to error in my internet connection!
2016-03-07T17:57:08+05:30
∠DAC =∠ BAC
∠DAC=∠BAC
but ∠DAC=∠BCA
so ∠DCA=∠CAB=∠DAC=∠BCA
so AB=BC=DA
so it is a rombus
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