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Mathematics

In the adjoining figure, find:

(i) the number of triangles pointing up.

(ii) the total number of triangles.

In the adjoining figure, find: Basic Geometrical Concepts, ML Aggarwal Understanding Mathematics Solutions ICSE Class 6.

Geometrical Concepts

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Answer

The adjoining figure shows a large equilateral triangle whose each side is divided into 3 equal parts, creating a network of 9 unit triangles inside it (6 pointing up and 3 pointing down).

Let us count the triangles of each size carefully.

(i) Triangles pointing up:

  • Size 1 (unit upward triangles): There are 6 unit upward triangles.
  • Size 2 (formed by 4 unit triangles together): There are 3 such upward triangles.
  • Size 3 (the whole large triangle): There is 1 such upward triangle.

Total triangles pointing upwards = 6 + 3 + 1 = 10.

∴ The number of triangles pointing up is 10.

(ii) Triangles pointing down:

  • Size 1 (unit downward triangles): There are 3 unit downward triangles.
  • No larger downward triangles exist in this figure.

Total downward triangles = 3

Total number of triangles = Triangles pointing up + Triangles pointing down

= 10 + 3 = 13

∴ There are total 13 triangles in the figure.

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