6th Grade Math Textbook, Fundamentals

Lesson 9-9 for exercise sets. &KDSWHU 

3UDFWLFH   $FWLYLWLHV

Here are some important relationships between

the sides and angles of triangles.

• In any isosceles triangle or equilateral
  triangle, angles opposite congruent sides are
  congruent. These are called.


• For all triangles, the angle with the greatest
  measure is opposite the longestside.


• For all triangles, the angle with the least
  measure is opposite the shortestside.

base angles

A

B

C

mA  mC

base

angles

shortest

side

longest

side

smallest

angle

largest

angle

You can use geometry software to explore congruent triangles.

Use software to draw any three line segments that could form a
triangle. Make a copy of the line segments you drew.

Use one set of the line segments. Join the line segments at their endpoints
to form a triangle. Then use the other set of line segments. Can you
join endpoints to make a triangle that is notcongruent to the first triangle?
Which statement discussed in this lesson is supported by this activity?

Which statement—SSS, SAS, or ASA—shows why the triangles are congruent?
Explain.

Solve. Use the diagram.

4.Find the missing side measurements.

5.Find mZXY. Explain your reasoning.

6.Discuss and Write Triangles FGH and JKLhave

three pairs of congruent corresponding angles.

Why might these triangles notbe congruent?

TU

SVR

M W

O N

P

D

E F

G

H

J

ABCZXY

A

Z

XY

BC

9 in.

8 in. 9 in. 8 in.

(3x  1) in.

(4x  2) in.

50

 59

n 59

71

71