$2.5+5.9+8.13+11.17+\ldots$ to 10 terms $=$

Question

Aicharya · Accepted Answer

Let $S=2.5+5.9+8.13+\ldots .+$ to 10 terms $\begin{aligned} & \Rightarrow S=\sum_{n=1}^{10}(3 n-1) \cdot(4 n+1)=12 \sum_{n=1}^{10} n^2-\sum_{n=1}^{10} n-\sum_{n=1}^{10} 1 \ & \Rightarrow S=4620-55-10=4555 . \end{aligned}$

$2.5+5.9+8.13+11.17+\ldots$ to 10 terms $=$

Solution