Geometry: An Interactive Journey to Mastery

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Lesson 15

Topics

x Classifying triangles via side lengths.

x Classifying triangles via angles.

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x acute triangle: A triangle with each of its three interior angles acute.

x obtuse triangle: A triangle with one interior angle that is an obtuse angle.

x right triangle: A triangle with one of its interior angles a right angle.

x scalene triangle: A triangle with three different side lengths.

Results

x Suppose that a triangle has three side lengths a, b, and c.

ż If a^2 + b^2 !c^2 , then the angle between the sides of lengths a and b is acute.

ż If a^2 + b^2 = c^2 , then the angle between the sides of lengths a and b is right.

ż If a^2 + b^2 c^2 , then the angle between the sides of lengths a and b is obtuse.

x The interior angle of largest measure in a triangle lies opposite the longest side of the triangle.

Summary

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lengths and via measures of interior angles.