NCERT Class 9 Maths Formula CBSE Board Sample Problems Part 6 (For CBSE, ICSE, IAS, NET, NRA 2022)

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6. Line and Angles

What is angle: An angle is a formed of two rays with a common endpoint. The Common end point is known as the vertex of the angle and the rays as the sides, sometimes as the legs and sometimes the arms of the angle

Types of Angles

Types of Angles
Angle TypeFigure
Acute Angle
Acute Angle
Obtuse Angle

Obtuse Angle
Right Angle

Right Angle
Reflex Angle

Reflex Angle
Straight Angle

Straight Angle
Types of Angles
S. noTermsDescriptions
1Complimentary AnglesTwo angles whose sum equal to
Complimentary Angles
2Supplementary AnglesTwo angles whose sum equal to 180°
Supplementary Angles
3Vertically Opposite anglesIf two lines intersect with each other, then vertically opposite angles are equal
Vertically Opposite Angles

4Transversal across the parallel LinesIf 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

5Theorem on Transversal across the linesIf a transversal intersects 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

6Parallel lines NoteLines which are parallel to a given line are parallel with each other

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