Question

pls help me pls please ​

Answer 1

Important concept:Sum of sqaure of first n natural no. =n(n+1)(2n+1)/6

of sqaure of first n natural no. =n(n+1)(2n+1)/6sum of first n natural number=n(n+1)/2

Now, let's move on question

Applying the above formula we get

n(n+1)(2n+1)/{2(n)(n+1)/2}=17

2n+1=17

n=8

now,

required sum S=(2×1-1)+(2×2-1)+(2×3-1)+......+(2×8-1)

S=1+3+5+.....+15

this is now in AP

so,apply the sum formula of AP

=n/2 ×(a+l)=4×(1+15)=64

Hence,the required sum is 64