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Triangles classified by angles In an acute triangle, all of the angles are acute. An obtuse triangle has one obtuse angle. A right triangle has one right angle.
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Sum of Angles in Triangles
Triangles classified by sides
A scalene trianglehas no congruent sides.
An isosceles trianglehas at least 2 congruent sides
An equilateral triangle, all of the sides are congruent.
Triangles classified by angles
In an acute triangle, all of the angles are acute.
An obtuse triangle hasone obtuse angle.
A right triangle has one right angle.
Classify each triangle according to its sides and angles.
EX1) Two congruent sides
acute Three acute angles
This is an acute isosceles triangle.
EX2)No congruent sides
right One right angle
This is a right scalene triangle.
isosceles
scalene
EX3) Three congruent sides
acute Three acute angles
EX4) No congruent sides
right One right angle
equilateral
scalene
EX5) Two congruent sides
obtuse One obtuse angle
EX6)Two congruent sides
right One right angle
isosceles
isosceles
Tear off the corners of your triangle and put them together.
The sum of the measures of the angles in a triangle is 180°.
m1 + m2 + m3 = 180° 1 3
2
Find the measure of the unknown angle.
55°
80° x
80° + 55° + x = 180°
135° + x = 180°–135° –135°
x = 45°
The sum of the measures of the angles is 180°.
EX7)
90° + 2x + x = 180° 90° + 3x = 180°
–90° –90°
3x = 90°
90°
x
2x
EX8)
3 = 3
x = 30°2x = 60°
AssignmentPage 6131-16
notes
Classify Triangles
Classify triangles by the lengths of their sides and their angles.
Date ______________
Triangles classified by sides
A scalene triangle
An isosceles triangle
An equilateral triangle,
Triangles classified by angles
In an acute triangle
An obtuse triangle has
A right triangle
Classify each triangle according to its sides and angles.
EX1)
EX2)
EX3)
EX4)
EX5)
EX6)
Find the measure of the unknown angle.
55°
80° x
EX7)
90°
30°
x
EX8)
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