**Line, line segment and ray** :

If we take a point and draw a straight path that extends endlessly on both the sides, then the straight path is called as a line.

A ray is a part of a line with one endpoint.

A line segment is a part of a line with two endpoints.

### Angles :

### Complementary Angles

When the sum of the two angles is 90°, the angles are called complementary angles.

e.g. ∠A = 40°, ∠B = 50°

∠A + ∠B = 40° + 50° = 90°

### Supplementary angles

When the sum of two angles is 180°, they are called supplementary angles.

e.g. ∠A = 130°, ∠B = 50°

∠A + ∠B = 130° + 50° = 180°

### Adjacent Angles

Two angles are adjacent, if they have

(i) A common vertex

(ii) A common arm

(iii) Their non-common arms on different sides of the common arm.

### Linear Pair

Linear pair of angles are adjacent angles whose sum is equal to 180∘.

### Transversal of Parallel Lines

(a) Corresponding angles are equal.

∠1 = ∠5, ∠3 = ∠7, ∠2 = ∠6, ∠4 = ∠8

(b) Alternate interior angles are equal.

∠3 = ∠6, ∠4 = ∠5

(c) Interior angles on the same side of transversal are supplementary.

∠3 + ∠5 = 180°, ∠4 + ∠6 = 180°.

NCERT Solutions