Help on sigma notation

[Bugandbear]

So I’ve been asked to write out the following in sigma notation. I believe I’m right on the second but having difficulty with the first and third. Any help would be greatly appreciated.

625 - 125 + 25 - 5 +....
End = infinite term= ? Start = ?

3 + 10 + 17 + 24 +....
end= infinite term= 7 start = 1

0 + 3 + 8 + 15 + 24 + 35
End = 5 term= ? Start = 0

struggling to find the term of each.

 

[Deleted member 4993]

So I’ve been asked to write out the following in sigma notation. I believe I’m right on the second but having difficulty with the first and third. Any help would be greatly appreciated.

625 - 125 + 25 - 5 +....
End = infinite term= ? Start = ?

3 + 10 + 17 + 24 +....
end= infinite term= 7 start = 1

0 + 3 + 8 + 15 + 24 + 35
End = 5 term= ? Start = 0

struggling to find the term of each.

625 - 125 + 25 - 5 +.... = 5⁴ - 5³ + 5² - 5¹ + ..........
End = infinite term= ? Start = ?

3 + 10 + 17 + 24 +.... = 3 + (3+7) + (3+2*7) + (3+3*7) .....
end= infinite term= 7 start = 1

0 + 3 + 8 + 15 + 24 + 35 = (1² - 1) + (2² -1) + (3² - 1) + (4² -1) + (5² -1) + (6² -1)......
End = 5 term= ? Start = 0

Please show us what you have tried and exactly where you are stuck.

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[Steven G]

You said that I believe I’m right on the second. That is great. Can we see your work?

To make the sign change you can use (-1)ⁿ or (-1)ⁿ⁺¹