Question

The sum of the n consecutive natural odd numbers starting from 5 is 45. Find the value of n.

Answer 1

Answer:

Step-by-step explanation:

5,7,9,…….. S(n)= 45. Найдите значение n.

аₙ=а₁+d(n-1),   d= а₂- a₁=7-5=2  ,    аₙ=5+2(n-1)=5+2 n-2=2 n+3  ,    

S(n)=( а₁+аₙ)* n\2.

45=( 5+2 n+3)* n\2,

90=8n+2 n²,

2 n²+8 n-90=0

n²+4n-45=0 , D=196 ,

n₁=5,   n₂=-9 не подходит.

Ответ n=5