Class 7 Chapter 10: Lines and Angles

Important Concepts and Formulas on Lines and Angles

1.      Lines that do not intersect each other are called parallel lines.

2.      Two distinct lines meeting at a point are called intersecting lines.

3.      A line intersecting two or more given lines in a plane at different points is called a transversal.

4.      If two parallel lines are cut by atransversal, then (i) each pair of alternate angles are equal (ii) each pair of corresponding angles are equal (iii) each pair of interior angles on the same side of transversal are supplementary.

5.      Three or more points are collinear if all of them lie on the same line.

6.      Three or more lines are concurrent if all of them pass through the same point, and the point is called the point of concurrence of the lines.

7.      A line which cuts the given line segment into two equal parts at 90º is called the perpendicular bisector.

8.      An angle is formed when two lines intersect each other at a point.

9.      Angle AOB is written as ∠AOB. Its vertex O is always written in the middle. OA and OB are called the arms of ∠AOB or ∠BOA.

10. Two adjacent angles have a common vertex, a common arm but no common interior points.

11. If the pairs of angles are adjacent and supplementary, then they form a linear pair.

12. When two lines intersect at a point, two pairs of vertically opposite angles are formed. Vertically opposite angles are always equal in measure.

13. If the sum of the measures of two angles is 90°, they form a pair of complementary angles.

14. If the sum of the measures of two angles is 180°, they form a pair of supplementary angles.