Question

If the sum of ‘n’ and ‘(n−1)’ terms of an A.P. is 441 and 356 respectively then the nth term of the A.P. is

Answer 1

Step-by-step explanation:

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Answer 2

Step-by-step explanation:

The sum of n terms Sn = 441

Similarly, Sn-1= 356

a = 13

d= n

For an AP, Sn = (n/2)[2a+(n-1)d]

Putting n = n-1 in above equation,

l is the last term. It is also denoted by an. The result obtained is:

Sn  -Sn-1 = an

So, 441-356 = an

an = 85 = 13+(n-1)d

Since d=n,

n(n-1) = 72

⇒n2 – n – 72= 0

Solving by factorization method,

n2-9n+8n-72 = 0

(n-9)(n+8)=0

So, n= 9 or -8

Since number of terms can’t be negative,

n= d = 9