Question

Sum of first n natural no. Is S ans S=n(n+1)/2. If S=55 then find value of n.

Answer 1

Answer:

10

Step-by-step explanation:

S= n/2+(2a+(n-1)d)

55= n/2 + (2 + (n-1))

110= 2n-n+n²

n²+n-110=0

n²+11n-10n-110=0

n(n+11) -10(n+11)=0

n= 10, -11

n≠ -11

so the value of n is 10

Answer 2

Step-by-step explanation:

55=n(n+1)/2

110=n²+n

n²+n-110=0

n²+11n-10n-110=0

n(n+11)-10(n+11)=0

n=10