Question

Need answers asap! I cannot figure it out at all.

Answer 1

Given:

`a_n=\sum_{k\mathop{=}1}^n2k+4`

Required:

`We\text{ need to find }a_4.`

Step-by-step explanation:

Consider the given equation.

`a_n=\sum_{k\mathop{=}1}^n2k+4`

Replace n =4 in the equation.

`a_4=\sum_{k\mathop{=}1}^42k+4`

Expand the summation.

`a_4=(2(1)+4)+(2(2)+4)+(2(3)+4)+(2(4)+4)`
`a_4=(2+4)+(4+4)+(6+4)+(8+4)`
`a_4=6+8+10+12`
`a_4=36`

Final answer:

`a_4=6+8+10+12`