# A polygon has 20 sides. The number of its diagonals will be:

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A polygon has 20 sides. The number of its diagonals will be:
1. 50
2. 120
3. 170
4. None of these.

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Correct Answer - Option 3 : 170

Concept:

A polygon made by joining n non-collinear points will have n sides and (nC2 - n) diagonals.

Calculation:

The polygon has n = 20 sides.

The number of diagonals will be: (20C2 - 20)

$\frac{20!}{2!\times18!}-20$

= 170.