Proof for Theorem
Prove: If a quadrilateral is an isosceles trapezoid, the diagonals are congruent.

thisos2given
thisos2pf
 
Statements
  
Reasons
1.
isos. trap. ABCD
1.
Given
2.
∠DABcongruent∠CBA
2.
An isos. trap. is a trapezoid with congruent base angles.
3.
thisos2pf3
3.
A trap. is a quad. with at least 1 pr. of parallel sides.
4.
thisos1pf9
4.
An isos. trap. has congruent legs.
Which we have proven true.
5.
thisos2pf5
5.
Reflexive property.
6.
thisos2pf6
6.
SAS - if 2 sides and the included < of 1Δ are congruent to the corres. parts of another Δ, the Δs are congruent.
7.
thisos2pf7
7.
CPCTC-corres. partscongruentΔs arecongruent.

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