in this ques m nt abl to undrstnd dat wat is it asking... the sum of n terms of an AP is 3n² +5. Find the number of terms which equals 159.

is the ans. 27

i think they r asking that if sum of n terms of an AP is (whatever....) then which term is 159 of that AP...i think 27th term

 Listen dear, the qstn is wrong i guess.

When u use 3n^2 + 5 = 159 we dont get n as an integer, This implies that the data of the qstn is wrong

There is another way to prove that the data is wrong

Lets take n=1, we should get the first term that is 8. When n=2, we get 17, then 32 with n=3. This is not an AP.

i think its question mistake 3n^2 +5n.......and then answer will be 27 .....and in this question somethings is missing....

@ priyanka she is right it  is sum of progression series ......i think question should be "the sum of n terms of an AP is 3n^2 +5n or 3n^2 +5 . and its Tn = 159 .then find "n" ?

S_n = 3n² + 5

S_n+1 = 3(n+1)²  + 5

T_n = S_n+1 - S_n

    = 3(n+1)²  + 5 - (3n² + 5)

    = 3(2n+ 1)

As per question,

3(2n+1)= 159

2n+1=53

n=26

hey ths question is wrng dear Sn=3n^2+5

ths means first term is 8

secnd term is 9 as sum of first 2 term is 17

thrd term is 15 as sum of first 3 term is 32

and i dnt thnk so tht ths form A.P

question is completly correct just answer is wrong ( correct answer =27) this question has been asked in DCE-CEE 1995 .....