10-4 Triangles10-4 Trianglespages 428-431pages 428-431

Indicators G3b- Use triangle sum relationships to solve problems.G4- Determine necessary conditions for congruence of triangles.

A triangle is a figure with three sides and three angles.

The sum of the measures of the angles of a triangle is always 180º.

1 + 2 + 3 = 180ºmm m2

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ExampleExampleAn airplane has wings that

are shaped like triangles.

Find the missing measure.

1 + 2 + 3 = 180º

112º + 47º + x = 180º

159º + x = 180º

- 159 - 159

x = 21º

mmm 112º

47ºxº

The measure of the wing’s third angle 21º.

Classify Triangles

Using Angles

Acute

All acute (<90º) angles

Right

1 right (90º) angle

Obtuse

1 obtuse (>90º) angle

Classify Triangles

Using Sides

Scalene

No congruent sides

Isosceles

At least 2 congruent sides

Equilateral

3 congruent sides

= =

=

Classify each given triangle by Classify each given triangle by angles and sidesangles and sides

acute, equilateral

acute, scalene

Right, scalene

acute, isosceles

Obtuse, scalene