Quadrilaterals Question
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Grade 10 Quadrilaterals CCSS: HSG-CO.C.11
Given: Quadrilateral ABCD with diagonal ¯BD where ¯AB || ¯CD and ¯BC || ¯AD
Prove: ∠BAD≅∠DCB

Statement | Reason |
1.¯AB || ¯CD | 1.Given |
2.∠ABD≅∠CDB | 2.Alternate interior angles are congruent |
3.¯BC || ¯AD | 3.Given |
4.∠ADB≅∠CBD | 4.Alternate interior angles are congruent |
5.m∠ABD=m∠CDB, m∠ADB=m∠CBD | 5.Definition congruent angles |
6.m∠ABD+m∠ADB+m∠BAD=180°, m∠CDB+m∠DCB+m∠CBD=180° | 6.Sum of angles in a triangle is 180° |
7.m∠CDB+m∠DCB+m∠CBD= m∠ABD+m∠ADB+m∠BAD | 7.Substitution Property of Equality |
8.m∠DCB=m∠BAD | 8. |
9.∠BAD≅∠DCB | 9.Definition of congruent angles |
- Elimination Property of Equality
- Corresponding angles are congruent
- Definition of congruent terms
- Subtraction Property of Equality