CBSE Class 9 Maths Lines and Angles
Basic Concepts of GeometryA line extends indefinitely in both the directions.
Ray has a fixed starting point but no ending point.Line segment has two end points.
According to Linear Pair axiom: If a ray stands on a line then the sum of the two angles formed is 180 degree. If two lines intersect each other then the vertically opposite angles formed are equal.
Parallel Lines and TransversalsTransversal is a line which intersects a pair of lines.
If two parallel lines are intersected by a transversal, then the corresponding angles formed are equal and vice versa.
If two parallel lines are intersected by a transversal, then the alternate interior angles formed are equal and vice versa.
Parallel Lines and Co-Interior AnglesIf two parallel lines are intersected by a transversal, then the interior angles on the same sides of the transversal are supplementary, and if the co-interior angles are supplementary then the lines are parallel.
If two lines are parallel to the same line then they are parallel to each other.
Angle Sum Property of A TriangleThe sum of the interior angles of any triangle is 180 degree.
Exterior angles of the triangle can be obtained by extending the sides of the triangle.
Each exterior angle is equal to the sum of the interior opposite angles.