Question

the sum of S of 1st n natural number is given by relation
S= n(n+1) ÷ 2
find n if sum is 55

Answer 1

Answer:

10

Step-by-step explanation:

n(n+1)/2 = 55

n(n+1) = 110

n^2 +n - 110 = 0

n^2 + 11n - 10n - 110 = 0

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

n = 10

n = -11 (not possible)

So n = 10