Question

Need a step by step explanation​

Answer 1

Answer:

$= \frac{2 {n}^{3} - 3 {n}^{2} - 5n + 10 }{2}$

Step-by-step explanation:

$= 3 \times \frac{n(n + 1)(2n + 1)}{6} - 6 \times \frac{n(n + 1)}{2} + 5 \\ \\ = \frac{n(n + 1)(2n + 1)}{2} - \frac{3(n)(n + 1)}{1} + 5 \\ \\ = \frac{n(n + 1)(2n + 1) - 6n(n + 1) + 10}{2} \\ \\ = \frac{n(2 {n}^{2} + 3n + 1) - 6 {n - 6n}^{2} + 10}{2} \\ \\ = \frac{2 {n}^{3} + 3 {n}^{2} + n - 6n - 6 {n}^{2} + 10}{2} \\ \\ = \frac{2 {n}^{3} - 3 {n}^{2} - 5n + 10 }{2}$