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Classifying Triangles & Angles of Triangles Sections 4-1 & 4-2
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Classifying Triangles & Angles of Triangles
Sections 4-1 & 4-2
A triangle is the figure formed by 3 segments joining 3 noncollinear points. Each of the 3 points is a vertex. The segments are the sides.
A
BC
CABCABSides ,,:
A, B, CVertices points:
Classifying Triangles by Sides
Scalene Triangle – no sides congruent
Isosceles Triangle – At least 2 sides congruent
Equilateral Triangle – All sides congruent
Classifying Triangles by Angles
Right – 1 right angle
Equiangular – all angles congruent
Acute – 3 acute angles
Obtuse – one obtuse angle
500 600
700
1200
400200
600600
600
Parts of an Isosceles Triangle
legleg
base
vertex angle
base angles
Angle Sum Theorem
The sum of the measures of the angles of a triangle is 180.
400400
1000
Third Angle Theorem
If 2 angles of one triangle are congruent to 2 angles of another triangle, then the third angles are congruent.
Corollariesstatements that can be easily proved using a theorem
Each angle of an equiangular triangle has measure 60.
In a triangle, there an be at most one right angle or obtuse angle.
The acute angles of a right triangle are complementary.
Exterior Angle TheoremThe measure of an exterior angle of a
triangle equals the sum of the measures of the 2 remote interior angles.
750
350
400Exterior
Remote interiorangles
Joke Time
What has wings and solves number problems?
A mothematician
What did one math book say to the other math book?
Don’t bother me! I’ve got my own problems!
What would a math student say to a fat parrot?
Poly-no-mial
