 # Triangle – a three sided polygon (straight sides; closed) A B C 3 sides: 3 angles: 3 vertices: A, B, C.

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triangle – a three sided polygon (straight sides; closed) A B C 3 sides: 3 angles: 3 vertices: A, B, C

Classify triangles by sides isosceles triangle – at least two sides are congruent D F E legs: base:

Classify triangles by sides scalene triangle – no sides are congruent

Classify triangles by sides equilateral triangle – all three sides are congruent

Classify triangles by angles acute triangle – all three angles are acute (less than 90º)

Classify triangles by angles right triangle – one right angle (exactly 90º) & two acute angles; the acute angles are complementary (they add up to 90°) KM L legs: hypotenuse:

Classify triangles by angles obtuse triangle – one obtuse angle (more than 90º) & two acute angles

Classify triangles by angles equiangular triangle – all three angles are congruent (60º)

altitude or “height” - a segment from a vertex perpendicular to the opposite side; may be inside, outside or on the triangle

median – “middle” – segment from a vertex to the midpoint of the opposite side; must be inside the triangle

angle bisector – segment from a vertex to the opposite side that bisects the angle

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