Triangle Vocabulary

Match the properties for each shape with the correct figure.

• Isosceles Triangle

• All 3 angles have measures less than 90degrees

• Acute Triangle

• 3 congruent sides and 3 congruent angles

• Obtuse Triangle

• 1 of the 3 angles has a measure greater than 90 degrees

• Right Triangle

• 2 congruent sides and 2 congruent angles

• Equilateral Triangle

• 1 of the 3 angles measures exactly 90 degrees

Match each definition with the appropriate term.

• Angle Bisector of a Triangle

• Perpendicular Bisector of a Triangle

• A segment that pases through the midpoint of a side and forms 90 degree angles

• Congruent Triangles

• This segment creates 2 congruent angles

• Triangle Midsegment

• 2 or more triangle whose corresponding parts are congruent

The sum of the measures of the angles in a triangles is equal to 180 degrees

• Triangle Angle Sum Theorem

• Triangle Mid-Angle Theorem

• Triangle Inequality Theorem

• Triangle Exterior ANgle Theorem

The measure of an exterior angle of a triangle is equal to the sum of the measures of the 2 non-adjacent interior angles inside the triangle

• Triangle Interior Angle Theorem

• Triangle Exterior Angle Theorem

• Triangle Side-Angle Theorem

• Triangle Non-Adjacent Angle Theorem

Triangle Inequality Theorem

• The sum of the lengths of any 2 sides of a triangle must be greater than the length of the third side

• The sum of the lengths of any 2 sides of a triangle can be equal to the length of the third side
• The sum of the lengths of any 2 sides of a triangle must be less than the length of the third side
• The sum of the lengths of any 2 sides of a triangle is irrelevant to the third side

A segment which extends from a vertex of the triangle and is perpendicular to the opposite side of the triangle

• Median
• Altitude
• Perpendicular bisector
• Angle bisector

A line segment whose endpoints are a vertex of the triangle and the midpoint of the opposite side

• Altitude
• Perpendicular bisector
• Bisector
• Median

Angle-Side Relationships in Triangles

• The size of an angle is unrelated to the opposite side
• The length of the opposite side determines the angle size
• The angle size is fixed regardless of side lengths
• The size of an angle directly corresponds to the length of the opposite side in a triangle

Scalene Triangle

• A scalene triangle is a triangle with one side longer than the others.
• A scalene triangle is a triangle with all sides of different lengths.
• A scalene triangle has all angles equal.
• A scalene triangle has at least two equal sides.