Warm Up

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Warm Up
Lesson Presentation
Lesson Quiz
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Warm Up Classify each angle as acute, obtuse, or
right. 1. 2. 3. 4. If the
perimeter is 47, find x and the lengths of the
three sides.
right
acute
obtuse
x 5 8 16 23
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Objectives
Classify triangles by their angle measures and
side lengths. Use triangle classification to find
angle measures and side lengths.
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Vocabulary
acute triangle equiangular triangle right
triangle obtuse triangle equilateral
triangle isosceles triangle scalene triangle
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Recall that a triangle ( ) is a polygon with
three sides. Triangles can be classified in two
ways by their angle measures or by their side
lengths.
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A, B, C are the triangle's vertices.
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Triangle Classification

By Angle Measures
Acute Triangle
Three acute angles
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Triangle Classification

By Angle Measures
Equiangular Triangle
Three congruent acute angles
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Triangle Classification

By Angle Measures
Right Triangle
One right angle
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Triangle Classification

By Angle Measures
Obtuse Triangle
One obtuse angle
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Class Example Classifying Triangles by Angle
Measures
Classify BDC by its angle measures.
?B is an obtuse angle.
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Class Example Classifying Triangles by Angle
Measures
Classify ABD by its angle measures.
?ABD and ?CBD form a linear pair, so they are
supplementary.
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Example 1 - 3
Classify EHG, EFH, FHG by its angle


measure
Triangle EHG is right Triangle EFH is obtuse
Triangle FHG is equiangular
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Triangle Classification

By Side Lengths
Equilateral Triangle
Three congruent sides
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Triangle Classification

By Side Lengths
Isosceles Triangle
At least two congruent sides
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Triangle Classification

By Side Lengths
Scalene Triangle
No congruent sides
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Class Example Classifying Triangles by Side
Lengths
Classify EHF by its side lengths.
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Class Example Classifying Triangles by Side
Lengths
Classify EHG by its side lengths.
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Example 1 - 3
Classify ABC, ABD and ACD by its side
lengths.
ABC equilateral Triangle ABD Scalene
Triangle ACD scalene
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Example 1 Using Triangle Classification
Find the side lengths of JKL.
Step 1 Find the value of x.
JK KL
4x 1.3 x 3.2
3x 4.5
x 1.5
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Example 1 Continued
Find the side lengths of JKL.
Step 2 Substitute 1.5 into the expressions to
find the side lengths.
JK 4x 1.3
4(1.5) 1.3 4.7
KL x 3.2
1(1.5) 3.2 4.7
JL 5x 0.2
5(1.5) 0.2 7.3
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Example 2
Find the side lengths of equilateral FGH.
Step 1 Find the value of y.
Given.
FG GH FH
Def. of ? segs.
Substitute (3y 4) for FG and (2y 3) for GH.
3y 4 2y 3
Add 4 and subtract 2y from both sides.
y 7
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Check It Out! Example 2 Continued
Find the side lengths of equilateral FGH.
Step 2 Substitute 7 into the expressions to find
the side lengths.
FG 3y 4
3(7) 4 17
GH 2y 3
2(7) 3 17
FH 5y 18
5(7) 18 17
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Homework

• Page 219 1-19

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Exit Question
Classify each triangle by its angles and
sides. 1. MNQ 2. NQP 3. MNP 4.
Find the side lengths of the triangle.
acute equilateral
obtuse scalene
acute scalene
29 29 23
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Exit Question Name
Classify each triangle by its angles and
sides. 1. MNQ 2. NQP 3. MNP 4.
Find the side lengths of the triangle.
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Exit Question Name
Classify each triangle by its angles and
sides. 1. MNQ 2. NQP 3. MNP 4.
Find the side lengths of the triangle.