Question

If the sum of the first n terms of an ap is 4n-n^2,wh@t is the first term(remember the first term is S1)?wh@t is the sum of first two terms?what is the second term? similarly, Find the 3rd,the 10th and the nth term..​

Answer 1

Answer:

Hope it helps....................

Answer 2

Answer:

• given ,

Sn = 4n -n^2

Just Think The Given Equation Of The Sum Of " n " Terms Is correct for all the terms in the AP , So If you put n=1 You get Sum of 1 terms which is actually the value of first term a1 .

It goes like this ,

Sn = 4n - n^2

= 4(1) - (1)^2

= 4 - 1 = 3

so The First Term Is 3.

Sum Of 2 Terms Is ...

S2 = 4(2) - (2)^2 = 4

Sum of first 2 Terms means a1 + a2 ,

Now you know a1 and S2 , so S2 - a1 = a2 = 4-3= 1

Now the common difference ,

a2- a1 = d = 1-3 = -2.

Hence The Basic Method Of Doing That was this .

Solving for a10 , an , a3 we get ,

a3 = -1 ;

a10 = -15;

an = 5 - 2n ;