### Chapter_4_Introduction_web

```Chapter 4.1 - Classifying Triangles
Objective: To be able to identify and classify
triangles by their angles and sides.
polygons (regular, non-regular, convex and
concave) using their properties.
Check.4.10 Identify and apply properties and
relationships of special figures (e.g., isosceles and
polygons, and solids).
Classifying Triangles
Classify by Angles
• Acute Triangle
• All angles < 90
• Obtuse Triangle
• One angle > 90
Classify by Sides
• Scalene Triangle
• No two sides are the same
• Isosceles Triangle
• At least two sides are the
same
• Equilateral Triangle
• Right Triangle
• One angle = 90
• All sides are the same
Acute Triangles
Classify the Triangles
A
• EDB
Right Triangles
B
C
D
•
•
•
•
ACD
ABC
DCE
BCE
Obtuse Triangles
E
• AEB
Isosceles Triangles
Classify the Triangles
A
• EDB
Equilateral Triangles
• none
B
C
E
Scalene Triangles
D
• AEB
• AED
• ACB
• ACD
• BCD
• DCE
Find Missing Values in Triangle
Find x and the measure of each side of the Equilateral
Triangle RST if RS = x + 9, ST = 2x, and RT = 3x -9
S
x+9
R
x + 9 = 2x
-x
-x
9 =x
2x
3x - 9
T
RS = x + 9
=9+9
= 18
Find Missing Values in Triangle
Find d and the measure of each side of the Equilateral
Triangle KLM if KL = d + 2, LM = 12 - d, and KM = 4d -13
L
d+2
K
12 - d
4d -13
M
d + 2 = 12 - d
+d
+d
2d + 2 = 12
-2
-2
2d = 10
d=5
KL = d + 2
=5+2
=7
Use the distance formula
• Find x and the measure of the sides of DEC. Classify
the triangle by its sides
E(-5, 3)
C (3, 9)
D (2, 2)
C
E
D
• Isosceles Triangle
Use the distance formula
• Find x and the measure of the sides of RST. Classify
the triangle by its sides
R(-1, -3)
S (8, -1)
T (4, 4)
T
R
• Scalene Triangle
S
RS = √85
ST= √41
RT= √74
Practice Assignment
• Block Page 239, 16 – 36 Every 4th and 44
• Honors page 239 30 – 52 Even
```