# NCERT Class 9 MathematicsGeometry Board Sample Problems

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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