Question:
How many sides are there in a polygon which has 20 diagonals?
How many sides are there in a polygon which has 20 diagonals?
Options:
- a) 6
- b) 7
- c) 8
- d) 10
- a) 6
- b) 7
- c) 8
- d) 10
correct answer : c)
Explanation:
Number of diagonals
= nC2 – n = 20
= nn n()- -1
2
= 20
Þ n2 – 3n – 40 = 0
Þ n = 8
Number of diagonals
= nC2 – n = 20
= nn n()- -1
2
= 20
Þ n2 – 3n – 40 = 0
Þ n = 8