Using Euler’s formula, find the unknown:

In first column, F = ?, V = 6 and E = 12
Using Euler’s formula, we see F + V – E = 2
F + V – E = 2
⇒ F + 6 – 12 = 2
⇒ F – 6 = 2
⇒ F = 2 + 6 = 8
Hence there are 8 faces.
In second column, F = 5, V = ? and E = 9
Using Euler’s formula, we see F + V – E = 2
F + V – E = 2
⇒ 5 + V – 9 = 2
⇒ V – 4 = 2
⇒ V = 2 + 4 = 6
Hence there are 6 vertices.
In third column, F = 20, V = 12 and E = ?
Using Euler’s formula, we see F + V – E = 2
F + V – E = 2
⇒ 20 + 12 – E = 2
⇒ 32 – E = 2
⇒ E = 32 – 2 = 30
Hence there are 30 edges.

Class 8 Maths Chapter 10 Exercise 10.3 Solution in Video

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