Step-by-step explanation:
In the attachment fig ABCD is a parallelogram with AC as diagonal.
we know that,
In a parallelogram opposite sides are equal and parallel
In a parallelogram sum of adjacent angles is 180°
that is
∠A+∠D= ∠B+∠C= 180°
Also, in a parallelogram opposite angles are equal.
So in ΔADC and ΔABC
1) AD=BC
2) DC= AB
And
3) ∠ADC= ∠ABC
therefore, ΔADC and ΔABC are congruent to each other and Emily was right.