NCERT Class 9 MathematicsGeometry Board Sample Problems (For CBSE, ICSE, IAS, NET, NRA 2022)
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Types of angles
| Acute Angle |  |
| Obtuse Angle |  |
| Right Angle |  |
| Reflex Angle |  |
| Straight Angle |  |
Complimentary Angles:
Two angles whose sum equal to
Supplementary Angles
Two angles whose sum equal to
Angles rules
Angles rules
Angles in a triangle add up to
So a + b + c =
Angles on a straight line add Up to
Angles in a quadrilateral add up to .
So
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
Vertically Opposite angles
If two lines intersect with each other, then vertically opposite angles are equal
Transversal across the parallel Lines
If the transversal intersect two 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