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Theorem: SAS Congruence Theorem
Theorem: ASA Congruence Theorem
Theorem: HL Congruence Theorem
m∠ θ+90^(∘)=180^(∘) ⇔ m∠ θ =90^(∘) Also, notice that these right triangles share their vertical side. Therefore, this side is congruent as well according to the Reflexive Property of Congruence.
Since two pairs of sides and the included angle are congruent, we can claim that the triangles are congruent by the SAS (Side-Angle-Side) Congruence Theorem. Now we can identify corresponding sides.
Since AB∥DC, by the Alternate Interior Angles Theorem we can claim that these angles are congruent. The triangles have two pairs of congruent angles, which means we know by the AA (Angle-Angle) Similarity Theorem that they are similar.
To claim congruence we also must show that at least one pair of corresponding sides is congruent. Notice that both triangles share BD as a side. Since this side is between the same two pairs of congruent angles, it shows two corresponding sides in our triangles.
Now we can claim congruence by the ASA (Angle-Side-Angle) Congruence Theorem. Note that AD and BC are corresponding sides, which means x=10.
Now we can claim congruence by the HL (Hypotenuse-Leg) Congruence Theorem, where ∠ CAB and ∠ ACD are corresponding angles.
With this information we can claim similarity by the AA Similarity Theorem. However, we do not have enough information about the side lengths. Therefore we do not have enough information to claim congruence, which means we cannot find x.