Prentice Hall Geometry

4-6 Congruence in Right Triangles

Quick Review

If the hypotenuse and a leg of one right triangle are congruent to the hypotenuse and a leg of another right triangle, then the triangles are congruent by the Hypotenuse-Leg (HL) Theorem.

Example

Which two triangles are congruent? Explain.

Triangle ABC has a right angle at A, one mark on side BC, and two marks on side AC. Triangle LMN has one mark on side MN and two marks on side LN. Triangle XYZ has right angle at X, one mark on YZ, and two marks on XZ.

Since cap delta eh b c  and cap delta x y z  are right triangles with congruent legs, and b c bar , approximately equal to . y z bar , comma . cap delta eh b c approximately equal to cap delta x y z  by HL.

Exercises

Write a proof for each of the following.

  1. Given: l n bar , up tack . k m bar , comma . k l bar , approximately equal to . m l bar

    Prove: cap delta k l n approximately equal to cap delta m l n

    Triangle KLM, with sides KL and ML equal, is divided in half by a line from L meeting KM at a right angle at N.

  2. Given: p s bar , up tack . s q bar , comma . r q bar , up tack . q s bar , comma . p q bar , approximately equal to . r s bar

    Prove: cap delta p s q approximately equal to cap delta r q s

    Triangles PSQ and RQS share side QS, with right angles at PSQ and RQS and sides PQ and RS equal.

4-7 Congruence in Overlapping Triangles

Quick Review

To prove overlapping triangles congruent, you look for the common or shared sides and angles.

Example

Separate and redraw the overlapping triangles. Label the vertices.

A figure has vertex D, E, F, and C has sides DE, EF, and FC, with angles E and F equal. Diagonals EC and DF intersect, with angles FEC and EFD equal. 

Triangle DEF has one arc at angle F and two arcs at angle E.

Triangle CFE has one arc at angle E and two arcs at angle F.

Exercises

Name a pair of overlapping congruent triangles in each diagram. State whether the triangles are congruent by SSS, SAS, ASA, AAS, or HL.

  1. Triangle ABE has sides AE and AB equal. Equal segments AD and AC extend from A to EB, with angles EAC and BAD equal.
  2. A figure has vertices F, I, H, and G, connected from left to right, with sides FI and HG equal and right angles at I and H. Diagonals FH and GI intersect.
  3. Figure PQRT is divided in half by vertical segment QT. From Q, segments lead to A on PT and S on RT, with sides AT and ST equal and angles QAT and QST equal.

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Table of Contents

Prentice Hall Geometry Chapter 1 Tools of Geometry Chapter 2 Reasoning and Proof Chapter 3 Parallel and Perpendicular Lines Chapter 4 Congruent Triangles Chapter 5 Relationships Within Triangles Chapter 6 Polygons and Quadrilaterals Chapter 7 Similarity Chapter 8 Right Triangles and Trigonometry Chapter 9 Transformations Chapter 10 Area Chapter 11 Surface Area and Volume Chapter 12 Circles Skills Handbook Reference Visual Glossary Selected Answers Index Acknowledgments