4.1 Triangles

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4.1 Triangles Angles
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A Triangle

• Is a figure formed by three segments
• Joining three noncollinear points.it has
• Sides..
• And Angles.

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Triangles can be classified by sides..

• Scalene (no sides equal)
• Isosceles (as least 2 sides equal)
• Equilateral (3 congruent sides)

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A Triangle can be classified by ANGLES

• Acute (3 acute angles)
• Right (1 right angle)
• Obtuse (1 obtuse angle)
• Equiangular (3 congruent angles)

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Triangle Vocabulary

• Vertex A
• Vertex B
• Vertex C

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Triangle Vocabulary

• Side opposite angle A
• Side opposite angle B
• Side opposite angle C

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Right Triangles

• Hypotenuse
• Leg
• Leg

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Isosceles Triangle

• Base
• Leg
• Leg

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When the sides of a triangle are extended.the
triangle has

• Interior Angles
• Exterior Angles

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Classify the triangle by its SIDES and Angles.
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Classify the triangle by its SIDES and Angles.
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Classify the triangle by its SIDES and Angles.
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Classify the triangle by its SIDES and Angles.
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Classify the triangle by its SIDES and Angles.
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Classify the triangle by its SIDES and Angles.
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Complete each sentence with the word always,
sometimes or never.
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Theorem 4.1-Triangle Sum Theorem

• The sum of the interior angles of a triangle is
  180 degrees.

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What is the measure of the numbered angle?
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What is the measure of the numbered angle?
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What is the measure of the numbered angle?
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Theorem 4.2-Exterior Angle Theorem

• The measure of an exterior angle of a triangle is
  equal to the sum of the two nonadjacent interior
  angles.

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A corollary to a theorem

• Is a statement that can be proved easily using a
  theorem
• Think of it as a mini-theorem.

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Corollary to the triangle sum theorem

• The acute angles of a right triangle are
  complementary.

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Assignment 4.1