NCERT Class 9 MathematicsGeometry Board Sample Problems
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Types of angles
Acute Angle |  Acute Angle Loading image••• |
Obtuse Angle |  Obtuse Angle Loading image••• |
Right Angle |  Right Angle Loading image••• |
Reflex Angle |  Reflex Angle Loading image••• |
Straight Angle |  Straight Angle Loading image••• |
Complimentary Angles:
Two angles whose sum equal to
Complimentary Angles
Supplementary Angles
Two angles whose sum equal to
Supplementary Angles
Angles rules
Angles rules
Angles in a Triangle
Angles in a triangle add up to
So a + b + c =
Angles on a Straight Line
Angles on a straight line add Up to
Angles in a Quadrilateral
Angles in a quadrilateral add up to.
So
Angles Around a Point
Angles around a point add up to.
So
If the side of the triangle is produced, the exterior angle formed is equal to the sum of the opposite interior angle
Triangle is Produced
Vertically Opposite angles
If two lines intersect with each other, then vertically opposite angles are equal
Vertically Opposite Angles
Transversal across the parallel Lines
If the transversal intersect two parallel lines
Transversal Across the Parallel Lines
a) Each pair of corresponding angles are equals
b) Each pair of alternate interior angles are equal
c) Each pair of interior angles on the same side of the transversal is supplementary
If a transversal intersect two lines such that either
a) Any one pair of corresponding angles are equal
b) Any one pair of alternate interior angles are equal
c) Any one pair of interior angles on the same side of the transversal is supplementary
Then the two lines are parallel
Parallel lines Note
Lines which are parallel to a given line are parallel with each other