Download Mr. Isosceles

Classifying triangles
Sec 4.1
Sol:
How many was can you classify a
triangle?
Angle sums in a triangle
The sum of the measures of the interior angles
and exterior angles of a triangle are 180°.
Hands on activity
Polygon – is a closed figure in a plane that is
made up of segments, called sides that
intersect only at their endpoints, called
vertices.
Triangle – is a three sided polygon. You name
them by their vertices.
Parts of a triangle
A
Sides
Vertices
C
B
Angles
Opposite Sides
The opposite side is the side that is across from
the angle. It is the side that has nothing to do
with forming the angle.
The side opposite A is _____
The side opposite B is _____
The side opposite C is _____
A
C
B
Classifying Triangles
 There are two ways to Classify Triangles.
1. By their Angles
a. Acute
b. Equiangular
c. Obtuse
d. Right
2. By the number of Congruent Sides they have.
a. Scalene
b. Isosceles
c. Equilateral
Acute triangle:
 All the angles are Acute (All the angles
measures are < (less than) 90°.
Mrs. Acute
A
C
B
Equiangular Triangle
 is a special type of Acute triangle.
All Angles are congruent.
Each angle has a measure of 60°.
Mrs. Equiangular
A
C
B
Obtuse Triangles
 Has only one angle that is obtuse.
 This angles has a measure > (greater than)
90° but < (less than) 180°.
Mr. Obtuse
A
C
B
Right Triangles
 Has only one angle that is a right angle.
Meaning only one angleA has a measure of 90°.
Mrs. Right
C
B
 The sides of a right triangle have special names:
Hypotenuse
a) The side opposite the right angle is the________________
Legs
b) The two sides that form the right angles are the_________
Use the triangle below, identify the
following:
Sides
Vertices
Angles
Hypotenuse
A
C
B
Legs
Scalene Triangle
 No two side are Congruent.
 Meaning all the side have different side
lengths.
Mr. Scalene
A
B
C
Isosceles Triangles
 At least two side are congruent.
Mr. Isosceles
CA = 3.36 cm
A
BA = 3.36 cm
B
C
Like a right Triangle the parts of an Isosceles
triangle have special names.
The angle formed by the
congruent sides is called the
VERTEX ANGLE
The two angles formed by
the base and one of the
congruent sides are called
BASE ANGLES.
The congruent sides are called
LEGS
leg
leg
The side opposite the vertex the
called the BASE
Equilateral Triangles
 All the sides are congruent.
 Is a special type of Acute triangle.
 Is also considered to be Isosceles.
Mr. Equilateral
B
A
C
Examples
Triangle PQR is an equilateral triangle. One side measures 2x + 5 and another
side measures x + 35. Find the length of each side.
R
2x + 5
P
x + 35
Q
Given STU, with vertices S(2, 3), T(4, 3) and
U(3, – 2) , use the distance formula to prove
STU is isosceles.
ST = ______________
TU = ______________
SU = ______________
Assignments
Classwork: Workbook Pg: 41 and 42 1-9
Homework: Pg 181-182 22-36