Question

Which expression is equivalent to *picture attached*

Answer 1

`\sum_(n=3)^(20)(n(n+1))=\sum _(n=3)^(20) n^2+ \sum _(n=3)^(20) n`

Explanation:

Given expression :
`\sum_(n=3)^(20)(n(n+1))`

Solving further :

`\Rightarrow \sum_(n=3)^(20)(n^2+n)`

`\Rightarrow \sum _(n=3)^(20) n^2+ \sum _(n=3)^(20) n`

So,
`\sum_(n=3)^(20)(n(n+1))=\sum _(n=3)^(20) n^2+ \sum _(n=3)^(20) n`

So, The given expression is equivalent to Option A

So, Option A is the answer