Question:
Very-Short and Short-Answer Questions
If the sum of first m terms of an AP is (2m2 + 3m) then what is its second term?
Solution:
Let Sm denotes the sum of first m terms of the AP.
$\therefore S_{m}=2 m^{2}+3 m$
$\Rightarrow S_{m-1}=2(m-1)^{2}+3(m-1)=2\left(m^{2}-2 m+1\right)+3(m-1)=2 m^{2}-m-1$
Now,
$m^{\text {th }}$ term of the AP, $a_{m}=S_{m}-S_{m-1}$
$\therefore a_{m}=\left(2 m^{2}+3 m\right)-\left(2 m^{2}-m-1\right)=4 m+1$
Putting m = 2, we get
$a_{2}=4 \times 2+1=9$
Hence, the second term of the AP is 9.