Question

B-2 the marked one plz give me the ans step by step

Answer 1

$Question:$

The sum 'S' of the first n natural numbers is given by the relation S = $\frac{n(n+1)}{2}$ . Find 'n' if S = 55.

$Solution :$

S = $\frac{n(n+1)}{2}$

⇒ 55 = $\frac{n(n+1)}{2}$

⇒ n² + n - 110 = 0

⇒ n² + 11 n - 10 n -110 = 0

⇒ n(n+11) -10(n+11) = 0

⇒ (n-10)(n+11) = 0

$\left \{ {{n=10} \atop {n=-11}} \right.$

• The possible value of n = 10 .

Thanks..