| When two lines meet at a point, that point becomes the vertex of an angle and the two lines become the angle’s sides. Often measured in degrees and in portions of degrees, angles are classified based upon their size: right angles equal 90 degrees; acute angles are less than 90 degrees; obtuse angles are greater than 90 degrees; and straight angles equal 180 degrees. As pictured (lower center and right), the three internal angles of an equilateral triangle are each 60 degrees, while the five internal angles of a regular pentagon are each 108 degrees. |
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