Download right triangle

Classify Triangles
Classify triangles by the lengths of their sides and
their angles.
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) isosceles Two congruent sides
acute
Three acute angles
This is an isosceles acute triangle.
EX2) scalene
right
No congruent sides
One right angle
This is a scalene right triangle.
EX3) equilateral
acute
EX4) scalene
right
Three congruent sides
Three acute angles
No congruent sides
One right angle
EX5) isosceles
Two congruent sides
obtuse
EX6) isosceles
right
One obtuse angle
Two congruent sides
One right angle
Tear off the corners of your triangle and put
them 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)
55°
80°
x
80° + 55° + x = 180° The sum of the measures
of the angles is 180°.
135° + x = 180°
–135°
–135° Subtract 135° from both sides.
x = 45°
The measure of the unknown angle is 45°.
EX8)
30°
90°
x
90° + 30° + x = 180° The sum of the measures
of the angles is 180°.
120° + x = 180° Combine like terms.
–120°
–120°
Subtract 120° from both sides.
x = 60°
The measure of the unknown angle is 60°.
notes
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