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
