NCERT Class 9 Maths Formula CBSE Board Sample Problems Part 6

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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 Type

Figure

Acute Angle

Acute Angle

Acute Angle

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Obtuse Angle

Obtuse Angle

Obtuse Angle

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Right Angle

Right Angle

Right Angle

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Reflex Angle

Reflex Angle

Reflex Angle

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Straight Angle

Straight Angle

Straight Angle

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Types of angles

S.no

Terms

Descriptions

1

Complimentary Angles

Two angles whose sum equal to

Complimentary Angles

Complimentary Angles

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2

Supplementary Angles

Two angles whose sum equal to 180°

Supplementary Angles

Supplementary Angles

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3

Vertically Opposite angles

If two lines intersect with each other, then vertically opposite angles are equal

Vertically Opposite angles

Vertically Opposite Angles

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4

Transversal across the parallel Lines

If the transversal intersect two parallel lines

Transversal across the parallel Lines

Transversal Across the Parallel Lines

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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

5

Theorem on Transversal across the lines

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

6

Parallel lines Note

Lines which are parallel to a given line are parallel with each other

Angles Rules

Angles in a triangle

Angles in a Triangle

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Angles in a triangle add up to

So a + b + c =

Angles on a straight line

Angles on a Straight Line

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Angles on a straight line add Up to

Angles in a quadrilateral

Angles in a Quadrilateral

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Angles in a quadrilateral add up to.

So

Angles around a point

Angles Around a Point

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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

Triangle is Produced

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