Question

2/N 162
(ii)
What is the sum of the first 10 natural numbers ?
(A) 55
(B)
20
(C)
65
(D) 11
(iii)
​

Answer 1

Answer:

S=

2

n(n+1)

⇒231=

2

n(n+1)

⇒n

2

+n−462=0

⇒n

2

+22n−21n−462=0

⇒n(n+22)−21(n+22)=0

⇒(n+22)(n−21)=0

⇒n=−22 or n=21

∴n=21 as n=−22 is not a natural number.