4'1 Classifying Triangles 111008

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4.1 Classifying Triangles 11/10/08

• A triangle polygon formed by three segments
  joining 3 noncollinear points.
• Can be classified by its sides and by its angles.

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Classification of Triangles by Angles

• Equiangular Triangle an acute triangle with all
  angles congruent.
• Acute triangle 3 acute angles
• Right Triangle 1 right angle
• Obtuse Triangle 1 obtuse angle

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Classification of Triangles by Sides

• Equilateral Triangles 3 congruent sides.
• Isosceles Triangles at least 2 congruent sides.
• Scalene Triangles- no congruent sides.

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Find Missing Values

• Find x and the measure of each side of
  equilateral triangle RST if RS x 9, ST 2x,
  and RT 3x 9.
• x 9 2x
• x 9
• RS x 9 ST 2x RT 3x 9
• 9 9 18 2(9) 18 3(9) 9 18
• For triangle RST, x 9, and the measure of each
  side is 18.

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Use the Distance Formula

• Find the measures of the sides of triangle DEC.
  Classify the triangle by sides. Point C (2 , 2)
  Point D (3 , 7), and Point E (-5 , 3).

Scalene Triangle