# 4.1 Triangles & Angles - PowerPoint PPT Presentation

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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)

• Vertex A

• Vertex B

• Vertex C

### Triangle Vocabulary

• Side opposite angle A

• Side oppositeangle B

• Side opposite angle C

• Hypotenuse

• Leg

• Leg

• Base

• Leg

• Leg

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

• Interior Angles

• Exterior Angles

### Theorem 4.1-Triangle Sum Theorem

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

### 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.