Thursday , July 7 2022

NCERT 5th Class (CBSE) Mathematics: Lines And Angle

Complementary angles

Two angles are complementary if the sum of their degree measures 90°.

(a) ∠a + ∠b = 90°

∠a and ∠b are complementary angles and they do not have to be adjacent to be complementary.

Complementary angles

(b) ∠c + ∠d = 90°

∠c and ∠d are adjacent complementary angles. If adjacent angles are complementary we call them adjacent complementary angles.

Complementary angles-b

Supplementary angles

Two angles are supplementary if the sum of their degree measures 180°

Supplementary angles

(a) ∠x + ∠y =180°

and ∠y are supplementary angles.

Angles do not have to be adjacent to be supplementary.

Supplementary angles-(a)

(b) ∠m + ∠n = 180°

∠m and ∠n are adjacent supplementary angles.

If adjacent angles are supplementary angles.

Supplementary angles-(b)

Vertically opposite angles

Look at this ironing board. The legs look like lines intersecting each other forming angles.

Interesting lines from pairs of vertically opposite angles.

∠COA  is vertically opposite ∠BOD

∠AOD is vertically opposite ∠COB

On measuring we find ∠COA = 100° and vertically opposite ∠BOD = 100°.

∠AOD = 80° and vertically opposite ∠COB = 80°.

Vertically opposite angles

Vertically opposite angles are equal.

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