Question

If the sum of the first n terms of an AP is given by Sn=4n sq- 3n , find the nth term of the AP.

Answer 1

Answer :

The sum of the 1st n terms of the AP = 4n² - 3n

⇒ Sn = 4n² - 3n

Now, the sum upto (n - 1) terms,

S(n - 1) = 4(n - 1)² - 3(n - 1)

= 4(n² - 2n + 1) - 3(n - 1)

= 4n² - 8n + 4 - 3n + 3

= 4n² - 11n + 7

Thus, the nth term of the AP

= Sn - S(n - 1)

= (4n² - 3n) - (4n² - 11n + 7)

= 4n² - 3n - 4n² + 11n - 7

= 8n - 7

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