Proof for Theorem
Prove: If a quadrilateral is an isosceles trapezoid, the opposite angles are supplementary.  |
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Statements |
Reasons |
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1. |
isos. trap. ABCD |
1. |
Given |
2. |
∠D  ∠C; ∠A ∠B |
2. |
An isos. trap. is a trapezoid with congruent base angles. |
3. |
 |
3. |
A trap. is a quad. with at least 1 pr. of parallel sides. |
4. |
∠D supp ∠A ∠B supp ∠C |
4. |
If 2 || lines are cut by a trans., the interior ∠s on the same side of trans. are supplementary. |
5. |
∠A supp ∠C ∠B supp ∠D |
5. |
Substitution |
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