Chapter Test
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Notice that we have two right triangles where a leg and the hypotenuse from each are congruent to the corresponding part of the other.
See solution.
Since AD and BD are congruent corresponding sides, it must be that △ ABD is an isosceles triangle where ∠ 1 and ∠ 2 are the base angles.
By the Base Angles Theorem, we know that ∠ 1 and ∠ 2 are congruent.