Kenneth S. answered • 12/16/17

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It surely helps to draw the figure. You will have two triangles, EAD & ECB.

Angles B & D are congruent...that's one angle in each triangle.

At E, there's a pair of congruent vertical angles...that's a second angle in each triangle.

The aforementioned two triangles are congruent, by "AA" and consequently

the third pair of corresponding angles, namely A and C, are congruent.

Q.E.D.