Angles and Lines in Geometry
Posted by
Ravi Kumar at Sunday, May 23, 2010
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The problems relating to geometry cover mostly triangles and circles. Even though polygons also are covered, the emphasis on polygons is not as much as on triangles and circles.
An angle of 90⁰ is a right angle; an angle less than 90⁰ is an acute angle; an angle between 90⁰ and 180⁰ is an obtuse angle; and angle between 180⁰ and 360⁰ is a reflex angle.
The sum of all angles on one side of a straight line AB at a point O by any number of lines joining the line AB at O is 180⁰. When any number of straight lines join at a point, the sum of all the angles around that point is 360⁰.
Two angles whose sum is 90⁰ are said to be complementary to each other and two angles whose sum is 180⁰ are said to be supplementary angles.
When two straight lines intersect, vertically opposite angles are equal. In the figure given alongside,