# Mind Map

## Lines and angles of Class 9

### If a ray stands on a line then the sum of two adjacent angles so formed is 180°.

• If two lines intersect each other, then the vertically opposite angles are equal.
• Acute angle measures between 0° and 90°.
• If a transversal intersects two parallel lines, then each pair of corresponding angles is equal
• If a transversal intersects two lines such that a pair of corresponding angles is equal, then the lines are parallel to each other.
• If a transversal intersects two parallel lines, then each pair of alternate interior angles is equal.
• If a transversal intersects two lines such that a pair of alternate interior angles is equal, then the two lines are parallel.➢ Two angles whose sum is 90° are called complementary angles.
• Interior angles on the same side of transversal are called co-interior angles.The sum of angles of a triangle is 180°.
• If a transversal intersects two parallel lines, then each pair of interior angles on the same side of transversal is supplementary.
• If a transversal intersects two lines such that a pair of interior angles on the same side of transversal is supplementary, then the two lines are parallel.
• If a side of a triangle is produced, then the exterior angle so formed is equal to sum of two interior opposite angles
• Lines which are parallel to the same line are parallel to each other.
• Right angle is exactly equal to 90°.
• Obtuse angle measures between 90° and 180°.
• Straight angle is exactly equal to 180°.
• Reflex angle measures between 180° and 360°.
• Complete angle is exactly equal to 360°.
• Two angles whose sum is 180° are called supplementary angles.
• Part of a line with two end paints is called a line segment.
• Part of a line with one end point is called a ray
• Three or more points lying on a line are called collinear points.
• An angle is formed when two rays are drawn in different directions from a common initial point.