Question

So I'm struggling with Sigma Notation and was hoping someone could help me with the question below. The lesson isn't very helpful.

Answer 1

You can do it as an arithmetic sequence, or...

Plug in n=3 into -5n-1
Plug in n=4 into -5n-1
Plug in n=5 into -5n-1
.
.
.
Plug in n=12 into -5n-1

Add them all together (that is what sigma notation means - sum all the things).

Answer 2

Indeed so in this case, the first is -16, the second, -21, -26, and so on until you end at -61.

Answer 3

So if I use the adding method I would just do
-5(3)-1=-16
-5(4)-1=-21
-5(5)-1=-26
-5(6)-1=-31
-5(7)-1=-36
-5(8)-1=-41
-5(9)-1=-46
-5(10)-1=-51
-5(11)-1=-56
-5(12)-1=-61
and then add them all to get -385?
Is that correct?

Answer 4

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Answer 5

Oh sweet. That's super simple. Thanks dude.

Answer 6

Yup, summations usually aren't very difficult (when they're like this).