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 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•••

Types of angles
S.no	Terms	Descriptions
1	Complimentary Angles	Two angles whose sum equal to Complimentary Angles Loading image•••
2	Supplementary Angles	Two angles whose sum equal to 180° Supplementary Angles Loading image•••
3	Vertically Opposite angles	If two lines intersect with each other, then vertically opposite angles are equal Vertically Opposite Angles Loading image•••
4	Transversal across the parallel Lines	If the transversal intersect two parallel lines Transversal Across the Parallel Lines Loading image••• 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