Question Number 66036 by aliesam last updated on 08/Aug/19
![](https://www.tinkutara.com/question/8920.png)
Answered by mr W last updated on 08/Aug/19
![=2(1+2+3+...+(n/2)) =2×(((1+(n/2))(n/2))/2) =((n(n+2))/4)](https://www.tinkutara.com/question/Q66043.png)
$$=\mathrm{2}\left(\mathrm{1}+\mathrm{2}+\mathrm{3}+…+\frac{{n}}{\mathrm{2}}\right) \\ $$$$=\mathrm{2}×\frac{\left(\mathrm{1}+\frac{{n}}{\mathrm{2}}\right)\frac{{n}}{\mathrm{2}}}{\mathrm{2}} \\ $$$$=\frac{{n}\left({n}+\mathrm{2}\right)}{\mathrm{4}} \\ $$