Question

H.W
Ex. (1) Find the sum of first n natural numbers.​

Answer 1

Step-by-step explanation:

S=2n(n+1)

⇒231=2n(n+1)

⇒n2+n−462=0

⇒n2+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.

Answer 2

Answer:

n×(n+1) /2 is the correct answer