Pre-Algebra Chapter 9
Pre-Algebra Chapter 9
Pre-Algebra Chapter 9
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Triangles can also be classified by their sides. Congruent sides have the<br />
same length.<br />
Study Tip<br />
Reading Math<br />
Tick marks on the sides of<br />
a triangle indicate that<br />
those sides are congruent.<br />
Scalene Triangle<br />
Isosceles Triangle<br />
Classify Triangles by their Sides<br />
Equilateral Triangle<br />
no congruent sides at least two sides congruent all sides congruent<br />
Example 3<br />
Classify Triangles<br />
Classify each triangle by its angles and by its sides.<br />
a. R<br />
Angles<br />
RST has a right angle.<br />
Sides<br />
T<br />
45˚<br />
45˚ RST has two congruent sides.<br />
S<br />
So, RST is a right isosceles triangle.<br />
b. G<br />
Angles<br />
GHI has one obtuse angle.<br />
35˚<br />
Sides<br />
120˚ 25˚<br />
I<br />
H GHI has no two sides that are congruent.<br />
So, GHI is an obtuse scalene triangle.<br />
Concept Check<br />
Guided Practice<br />
GUIDED PRACTICE KEY<br />
1. Compare an isosceles triangle and an equilateral triangle.<br />
2. Name a real-world object that is an equilateral triangle.<br />
3. OPEN ENDED Draw an obtuse isosceles triangle.<br />
Find the value of x in each triangle. Then classify each triangle as acute,<br />
right, or obtuse.<br />
4. 5. 6.<br />
72˚<br />
83˚<br />
x˚<br />
61˚<br />
x˚<br />
29˚<br />
48˚<br />
x˚<br />
27˚<br />
Classify each indicated triangle by its angles and by its sides.<br />
7. 8. 9.<br />
45˚<br />
90˚<br />
45˚<br />
110˚<br />
Lima Youngstown<br />
Ohio<br />
Cincinnati<br />
45˚<br />
25˚<br />
75˚<br />
75˚<br />
Application<br />
www.pre-alg.com/extra_examples<br />
10. ALGEBRA Triangle EFG has angles whose measures are in the ratio 2:4:9.<br />
What are the measures of the angles?<br />
30˚<br />
Lesson 9-4 Triangles 455
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