Class 8 · Chapter 11

Exploring Some Geometric Themes

Angles in polygons, tessellations, transformations.

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Ganita Prakash · Class 8 Part 2 (2026-27)

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Detailed theory

Triangulate an

n

-gon into

n-2

triangles → sum is

(n-2)\cdot 180°

. For regular, divide by

n

Key concepts & formulas

Interior angle sum of

n

-gon:

(n-2)\times 180°

Each interior angle of regular

n

-gon:

(n-2)\cdot 180°/n

Exterior angle of regular

n

-gon:

360°/n

; sum

= 360°

always.

Transformations: translation, rotation, reflection preserve shape.

Tessellations use these transformations.