Question

2+-3+4+-5+6 in sigma notation?

Answer 1

well, let's start simple. how would you express that if every number were positive? i.e. 2+3+4+5+6?

Answer 2

oh sorry my computer froze. If all the numbers were positive? +1

Answer 3

right, how would you write 2+3+4+5+6 in sigma notation?

Answer 4

um is that possible to do on a computer?

Answer 5

well you can just describe the lower and upper limits of the sigma and then the expression inside

Answer 6

OK well I'm new to this but lower would be 1 and upper 5 right?

Answer 7

are you learning from a book or some other reference that describes how to use sigma notation?

Answer 8

my teacher? who isn't here right now. Oh and the expression would be n+1

Answer 9

\[\sum_{1}^{5} n+1\]

Answer 10

yes, that's one way of doing it. ok, now we need to add something to that expression so that every other one is negative, any ideas on how to do that?

Answer 11

well in order to have the next number be negative, you have to be adding a negative number right?

Answer 12

right. so how can we turn every other number negative? i'll give you a hint ... you want to multiply the first number by 1, the second by -1, the third by 1 again, etc.

Answer 13

a hint? so you do know the answer...OK.

Answer 14

well what you just said is the part that confuses me. How can you multiple some numbers by -1, and others by +1? It's all 1 function right?

Answer 15

yes, i just thought you'd want to learn instead of only getting the answer

Answer 16

haha yeah I guess

Answer 17

It's just the last problem so I'm anxious

Answer 18

multiplying by -1 will alternate between positives and negatives

Answer 19

it is all one function but, i'll give you another hint ... what's (-1) squared?

Answer 20

1...

Answer 21

and what's -1 cubed?

Answer 22

-1

Answer 23

..oh.

Answer 24

and to the 4th power?

Answer 25

there you go, you cracked it. now put that together with your other expression.

Answer 26

yeah. got it.

Answer 27

excellent

Answer 28

thank you!

Answer 29

you're welcome, thanks for learning instead of just asking for the answer.

Answer 30

\[\sum_{1}^{5}\][(-1)^(n+1)]*(n+1)