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Transcript
Sum of Angles in Triangles
Triangles classified by sides
A scalene triangle
has no congruent sides.
An isosceles triangle
has 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 has
one obtuse angle.
A right triangle
has one right angle.
Classify each triangle according to its sides
and angles.
EX1) acute
isosceles
EX2) right
scalene
EX3) acute
equilateral
EX4) right
scalene
EX5) obtuse
isosceles
EX6) right
isosceles
Tear off the corners of your triangle and put the
corners together.
The sum of the
measures of the angles
in a triangle is 180°.
2
m1 + m2 + m3 = 180°
1
3
Find the measure of the unknown angle.
EX7) 80° + 55° + x = 180°
55°
135° + x = 180°
–135°
–135°
x=
EX8)
80°
45°
x
90° + 2x + x = 180°
90° + 3x = 180°
–90°
–90°
x
3x = 90°
3
=
3
x = 30°
2x = 60°
90°
2x
Essential Question
Describe the process to find the missing
angle in a triangle.
Assignment
Page 613
1-16
Date ______________
Classify Triangles
Classify triangles by the lengths of their sides and
their angles.
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.
EX7)
55°
80°
x
EX8)
30°
90°
x