Question

Write the series in summation notation:

-3 + 6 - 9 + 12 - 15

Answer 1

A way to take care of the alternating signs (i.e. + - + - ) is to use the factor \(\large (-1)^n\) since:
\(\large (-1)^1=-1\)
\(\large (-1)^2=1\)
\(\large (-1)^3 =-1\)
\(\large (-1)^4=1\)
etc..

Now you need to worry about going from 3 to 6 to 9 to 12 to 15. Hopefully you notice that this is simply multiplying by 3 every time. So, you can write this as \(3n\), were \(n\) will take on the values 1, 2, 3, 4, 5.
So, the sum becomes:
\[ \large \sum_{n=1}^5 (-1)^n(3n)\]

Answer 2

how about ∑5k = 1[8(k + 1)]

Answer 3

are you trying to evaluate tat?

Answer 4

yes

Answer 5

what is the summation running from? like going from k = ? to ?

Answer 6

5??

Answer 7

@MaimiGirl