. If the sum of the first n terms of an AP is


4n-n2 what is the first term (that is S1)? Whatis the sum of first two terms? What is the second term? Similarly, find the 3rd, the 10th andthe nth terms.

Best Answer

Solution:We can find the first term as follows:

S1 = 4 × 1 - 12 = 3

Now; sum of first two terms can be calculated as follows:

S2 = 4 × 2 - 22

= 8 - 4 = 4

Hence; second term = 4 – 3 = 1

And d = 1 – 3 = - 2

So, 3rd term can be calculated as follows:

a3 = a + (n – 1)d

= 3 + 2( - 2) = 3 – 4 = - 1

Similarly, 10th term can be calculated as follows:

a10 = a + 9d

= 3 + 9(- 2)

= 3 – 18

= - 15

 

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