Class 11

Math

Algebra

Sequences and Series

If the sum of the first n terms of an A.P. is given by the equation $n_{2}+7n$, then what is the first term and second term?

- $8$ and $10$
- $6$ and $12$
- $4$ and $8$
- $12$ and $8$

$∴S_{1}=a_{1}=1_{2}+7.1=8$ .......( 1 )

$∴S_{2}=a_{1}+a_{2}=2_{2}+7.2=18$ .......( 2 )

$∴a_{2}=S_{2}−S_{1}=18−8=10$ .......( 3 )

$∴a_{1}=8$ and $a_{2}=10$