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raytiller1 Group Title am i right? A store displays six computers on a shelf side–by–side. If the first computer is eight inches wide and each successive computer is four inches wider than the previous one, find the total width of the computers on the shelf. Part 1: Describe the sigma notation used in answering the question above. (2 points) Part 2: Show all your work and answer the question. (3 points) 2 years ago 2 years ago

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1. raytiller1 Group Title

8 ∑ 4 + 4n n=1 ∑ 4 + 4n = 4 ∑ 1 + n 4 * 8 + 4 ∑ n 32 + 4 [8 * 9 / 2] 32 + 40 72 inches

2. jim_thompson5910 Group Title

no, the answer is not $\Large \sum_{n=1}^{8}4+4n$ for part 1 Part 2 depends on part 1, so that is also incorrect

3. raytiller1 Group Title

ok can you help me then @jim_thompson5910

4. jim_thompson5910 Group Title

How many computers are we talking about here?

5. raytiller1 Group Title

6

6. jim_thompson5910 Group Title

so you're not summing to 8 up at the top (of the sigma), you're summing to 6

7. raytiller1 Group Title

thats the problem above says so i guess so

8. jim_thompson5910 Group Title

so it should be $\Large \sum_{n = 1}^{6}4+4n$ for part 1

9. raytiller1 Group Title

so is the first and 2nd part for part 2 right?

10. jim_thompson5910 Group Title

first part is, but the second is not...and you'd have to use 6 instead of 8

11. raytiller1 Group Title

∑ 4 + 4n = 4 ∑ 1 + n 4 * 6 + 4 ∑ n 24 + 4 [6 * 7 / 2] 24 + 25 49 inches

12. raytiller1 Group Title

?

13. jim_thompson5910 Group Title

4 [6 * 7 / 2] doesn't become 25

14. raytiller1 Group Title

84? i added thats why

15. raytiller1 Group Title

108 inches ?

16. jim_thompson5910 Group Title

it is 108 inches

17. jim_thompson5910 Group Title

108 is the total final answer for part 2

18. raytiller1 Group Title

can you help me with another problem?

19. jim_thompson5910 Group Title

sure, what is it

20. raytiller1 Group Title

help me with the steps i have an answer just don't know how? geometric partial sum ∑[i=1,5,3(-4)^(i-1)].

21. raytiller1 Group Title

nevermind i found it

22. jim_thompson5910 Group Title

You're basically summing 3(-4)^(i-1) from i = 1 to i = 5 So add up 3(-4)^(i-1) five times like so 3(-4)^(i-1) 3(-4)^(i-1) 3(-4)^(i-1) 3(-4)^(i-1) 3(-4)^(i-1) Then replace the first i with 1, the second i with 2, the third with 3, etc etc like this 3(-4)^(1-1) 3(-4)^(2-1) 3(-4)^(3-1) 3(-4)^(4-1) 3(-4)^(5-1) Now evaluate

23. raytiller1 Group Title

but i do need help with What is the 5th partial sum of ∑[i=1,∞,-1+5n]

24. raytiller1 Group Title

the answer i got for the last problem was 11,170

25. jim_thompson5910 Group Title

same thing, but you're now doing it with -1+5n

26. raytiller1 Group Title

i got 60 ?

27. jim_thompson5910 Group Title

write out -1+5n five times -1+5n -1+5n -1+5n -1+5n -1+5n then replace the first n with 1, the second with 2, etc etc to get -1+5(1) -1+5(2) -1+5(3) -1+5(4) -1+5(5)

28. jim_thompson5910 Group Title

Evaluate each piece, then add them all up

29. raytiller1 Group Title

70?

30. jim_thompson5910 Group Title

yes, you are correct the answer is 70