00:01
In this problem, we are told that ad is congruent to bc, and also that ad is parallel to bc.
00:10
Now, we see that if ad and bc are parallel, then we have these lines dc and bc that are intersecting two parallel lines.
00:23
And by the alternating angles theorem, we know that the measure of angle a and the measure of angle c are the same.
00:32
And similarly, the measure of angle b and d are also the same.
00:40
And now we can use this to see that if we drew a diagonal between b and d, then we can figure out that this diagonal would be the same for triangle a, d, b, as it is for triangle c -d -b, and therefore, since they have the same angle, and the same side, that means, well, we have the same angle, say angle a and then angle c...