# USING CONGRUENT TRIANGLES WORKSHEET

Problem 1 :

In the diagram shown below, AB || CD, BC || DA. Prove that

AB ≅ CD

Problem 2 :

In the diagram shown below,

A is the midpoint of MT

A is the midpoint of SR

Prove that MS || TR.

Problem 3 :

In the diagram shown below,

∠1 ≅ ∠2

∠3 ≅ ∠4

Prove that ΔBCE  ≅  ΔDCE.

Plane for Proof :

Show that ΔABD ≅ ΔCDB. Then use the fact that corresponding parts of congruent triangles are congruent.

First copy the diagram and mark it with the given information. Then mark any additional information that we can deduce. Because AB and CD are parallel segments intersected by a transversal, BC and DA are parallel segments intersected by a transversal, we can deduce that two pairs of alternate interior angles are congruent.

Mark Given Information :

Paragraph Proof :

Because AB || CD, it follows from the Alternate Interior Angles Theorem, that ∠ABD ≅ ∠CDB. For the same reason, ∠ADB ≅ ∠CBD, because BC || DA. By the Reflexive Property of Congruence, BD ≅ BD. We can use the ASA congruence postulate to conclude that

ΔABD ≅ ΔCDB

Finally, because corresponding parts of congruent triangles are congruent, it follows that

AB ≅ CD

Plane for Proof :

Prove that ΔMAS ≅ ΔTAR. Then use the fact that corresponding parts of congruent triangles are congruent to show that ∠M ≅ ∠T. Because these angles are formed by two segments intersected by a transversal, we can conclude that MS || TR.

 StatementsA is the midpoint of MT A is the midpoint of SRMA ≅ TA, SA ≅ RA∠MAS ≅ ∠TARΔMAS  ≅  ΔTARaaaaaaaa∠M ≅ ∠Taaaaaaa aaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaMS || TR ReasonsGivenGivenDefinition of midpointVertical Angles TheoremSAS Congruence PostulateCorresponding parts of congruent triangles are congruent. Alternate Interior Angles Converse

Plane for Proof :

The only information we have about ΔBCE and ΔDCE is that ∠1 ≅ ∠2 and that CE ≅ CE. Notice, however, that sides BC and DC are also sides of ΔABC and ΔADC. If we can prove that ΔABC ≅ ΔADC, we can use the fact that corresponding parts of congruent triangles are congruent to get a third piece of information about ΔBCE and ΔDCE.

 Statements∠1  ≅  ∠2∠3  ≅  ∠4AC  ≅  ACΔABC  ≅  ΔADCBC  ≅  DCCE  ≅  CEΔBCE  ≅  ΔDCE ReasonsGivenGivenReflexive Property of CongruenceASA Congruence PostulateCorresponding parts of ≅ Δ are ≅Reflexive Property of CongruenceSAS Congruence Postulate

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