4.1 Triangles & Angles
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4.1 Triangles & Angles. A Triangle. Is a figure formed by three segments Joining three noncollinear points ….it has Sides ….. And Angles. Triangles can be classified by sides. Scalene (no sides equal) Isosceles (as least 2 sides equal) Equilateral (3 congruent sides).

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4.1 Triangles & Angles

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4.1 Triangles & Angles


A Triangle

  • Is a figure formed by three segments

  • Joining three noncollinear points….it has

  • Sides…..

  • And Angles.


Triangles can be classified by sides..

  • Scalene (no sides equal)

  • Isosceles (as least 2 sides equal)

  • Equilateral (3 congruent sides)


A Triangle can be classified by ANGLES…

  • Acute (3 acute angles)

  • Right (1 right angle)

  • Obtuse (1 obtuse angle)

  • Equiangular (3 congruent angles)


Triangle Vocabulary

  • Vertex A

  • Vertex B

  • Vertex C


Triangle Vocabulary

  • Side opposite angle A

  • Side oppositeangle B

  • Side opposite angle C


Right Triangles

  • Hypotenuse

  • Leg

  • Leg


Isosceles Triangle

  • Base

  • Leg

  • Leg


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

  • Interior Angles

  • Exterior Angles


Classify the triangle by it’s SIDES and Angles.


Classify the triangle by it’s SIDES and Angles.


Classify the triangle by it’s SIDES and Angles.


Classify the triangle by it’s SIDES and Angles.


Classify the triangle by it’s SIDES and Angles.


Classify the triangle by it’s SIDES and Angles.


Complete each sentence with the word always, sometimes or never.


Click here to explore


Click here to explore


Theorem 4.1-Triangle Sum Theorem

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


What is the measure of the numbered angle?


What is the measure of the numbered angle?


What is the measure of the numbered angle?


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.


A corollary to a theorem

  • Is a statement that can be proved easily using a theorem

  • Think of it as a mini-theorem.


Corollary to the triangle sum theorem

  • The acute angles of a right triangle are complementary.


Assignment 4.1


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