Kageyama T.
asked 05/14/21Proving in Geometry
Given: AB ∥ DE
Prove: ΔABC ≅ ΔEDC
The figure is like an hourglass and the midpoint C.
What is the reason/theorem in these given statements:
AB ∥ DE -
∠A ≅ ∠E ; ∠B ≅ ∠D -
∠1 ≅ ∠2 -
ΔABC ≅ ΔEDC -
1 Expert Answer
William W. answered 05/14/21
Experienced Tutor and Retired Engineer
It would be super useful to see the picture that goes with this problem because with the information given, it is not possible to prove the triangle are congruent as there are no sides listed. Proving triangles are congruent requires one of the following:
SSS (side-side-side)
SAS (side-angle-side)
AAS (angle-angle-side)
ASA (angle-side-angle)
HL (for right triangles only and stands for hypotenuse-leg)
Notice that every one of these has a side included.
I will tell you this much. The reasons for AB ∥ DE is "Given" and the reasons for ∠A ≅ ∠E ; ∠B ≅ ∠D is "Alternate Interior Angles Theorem". Most likely the reason for ∠1 ≅ ∠2 is the "Vertical Angles Theorem".
But beyond that, without seeing the picture, I can't help since at least one set of corresponding sides must be congruent to prove triangle congruence (the proof needs another line in it that states two sides are congruent).
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Philip P.
OK, given that type of figure it's easy to show that all of the angles in the two triangles are congruent, which makes the two triangles similar but not necessarily congruent. All of the congruency theorems involve at least one side: SSS, SAS, ASA, AAS. Hence the problem needs to state that at least one side in triangle ABC is congruent to a side in EDC. Is there a given about sides being congruent? Look at the figure. Do two sides have a little slash though them? That means they're congruent.05/14/21