Question

If (1+3+5+..... upto n terms)/(2+5+8+....... upto 8 terms) = 9 , then find the value of n

Answer 1

Here, a=1 and d=2 and term=n
Sn=n/2(2+(n-1)2)
=n*n
Now in second, a=2,d=3,n=8
Sn=8/2(4+7*3)=4(4+21)=100
ATQ,n*n/100=9 or n*n=900 or n=30

Answer 2

Answer:30

Step-by-step explanation:

in 1+3+5.....nth term

a=1 , c.d=2

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

 =n/2 {2(1)+(n-1)2}

 =n/2 {2+2n-2}

 =n/2 {2n}

 =n^2

in 2+5+8............8th term

a=2 , c.d=3

S8=n/2 (2a+(n-1)d)

    = 8/2 {2(2)+(7)3}

    =4{4+21}

    =4(25)

    =100

now

n^2/100 = 9

n^2=900

n=$\sqrt[n]{x} 900$

n=30