# 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

Angle Type | Figure |

Acute Angle | |

Obtuse Angle | |

Right Angle | |

Reflex Angle | |

Straight Angle |

S.no | Terms | Descriptions |

1 | Complimentary Angles | Two angles whose sum equal to |

2 | Supplementary Angles | Two angles whose sum equal to 180° |

3 | Vertically Opposite angles | If two lines intersect with each other, then vertically opposite angles are equal |

4 | 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 |

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 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