Question

If the sum of first $n$ terms of a series be $5n^2+2n$ , then its second term is:

• A. $16$
• B. $17$
• C. $\frac{27}{14}$
• D. $\frac{56}{15}$

Answer 1

The correct option is B $17$

$S_n=5n^2+2n\left(\text{Given}\right)$

First term $\left(S_1\right)=5\cdot {\left(1\right)}^2+2\cdot 1=7$

Sum of first two terms $\left(S_2\right)=5\cdot {\left(2\right)}^2+2\cdot 2=24$

Therefore,

Second term $=S_2-S_1=24-7=17$