Question

Write the related series for the finite sequence –7, –10, –13, . . ., –22. then find the sum. –7 + (–10) + (–13) + (–16) + (–19) + (–22) = –87



–7 + (–10) + (–13) + (–15) + (–18) + (–22) = –85
–7 + (–10) + (–13) + (–14) + (–18) + (–22) = –84
–7 + (–10) + (–13) + (–17) + (–20) + (–22) = –89

Answer 1

I would say the last one, -7+(-10)+(-13)+(-17)+(-20)+(-22)=-89 , it seems the most reasonable since you go up by -3, hope this is correct and helps if not i apologize 

Answer 2

Answer:
`-7+(-10)+(-13)+(-16)+(-19)+(-22)=-87`

Explanation:

Given finite sequence : -7, -10, -13, . . ., -22.

Difference between first and second term=
`-10-(-7)=-10+7=-3`

Difference between second and third term =
`-13-(-10)=-13+10=-3`

Hence, the common difference = -3

The next term after -13 =
`-13+(-3)=-13-3=-16`

The next term after -16 =
`-16+(-3)=-16-3=-19`

The next term after -19 =
`-19+(-3)=-19-3=-22`.........which is the last term of the sequence.

Now, the sum of the given sequence =
`-7+(-10)+ (-13) + (-16) + (-19) + (-22)`

`=-7-10-13-16-19-22= -87`