Question

I need help with summation notation. Look at picture

Answer 1

`=18`

Explanation:

`\sum _(j=1)^33j`

Apply the constant multiplication rule:

`=3\cdot \sum _(j=1)^3j`

`\sum _(j=1)^3j`

Apply sum formula:

`=(1)/(2)\cdot \:3\left(3+1\right)`

`(1)/(2)\cdot \:3\left(3+1\right)`

`=3\cdot \:4\cdot (1)/(2)\\`

`=(1\cdot \:3\cdot \:4)/(2)`

`=(12)/(2)`

`=6`

`=3\cdot \:6`

`=18`