Question

the sum of first n terms of an AP is 3n^2-5,find the third term of the AP.​

Answer 1

Answer:hope it is helpful...

Step-by-step explanation:

Answer 2

The third term is 15.

Step-by-step explanation:

Given : The sum of first n terms of an AP is $3n^2-5$.

To find : The third term of the AP ?

Solution :

The sum of first n terms of an AP is

$S_n=3n^2-5$

Put n=1,

$S_1=3(1)^2-5$

$S_1=-2$

The first term is -2.

Put n=2,

$S_2=3(2)^2-5$

$S_2=7$

The sum of first and second term is 7.

i.e. $a_1+a_2=7$

$-2+a_2=7$

$a_2=9$

The second term is 9.

Put n=3,

$S_3=3(3)^2-5$

$S_3=22$

The sum of first, second and third term is 22.

i.e. $a_1+a_2+a_3=22$

$7+a_3=22$

$a_3=15$

The third term is 15.

#Learn more

Sum of the first m terms of an ap is n and sum of the first n terms of an ap is m show that the sum of first m+n terms is -(m+n)

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