Question

In figure, state which lines are parallel and why?

Answer 1

We know, If a transversal intersects two lines such that a pair of alternate interior angles are equal, then the two lines are parallel 

From figure: 

∠EDC = ∠DCA = 100° 

Lines DE and AC are intersected by a transversal DC such that the pair of alternate angles are equal. 

So, DE || AC.