Posted by **Anonymous** on Sunday, November 1, 2009 at 10:26am.

I have absolutely no idea how to do this please help!

Find the sum:

it has the sigma sign with 12 at the top, (10k-8)(6k+7) in the middle and k=1 at the bottom

- math- Algebra 2 -
**jim**, Sunday, November 1, 2009 at 10:51am
It just means, add:

the value of (10k-8)(6k+7) when k=1

plus

the value of (10k-8)(6k+7) when k=2

plus

the value of (10k-8)(6k+7) when k=3

plus

... (and so on, 4, 5, to 9, 10)...

the value of (10k-8)(6k+7) when k=11

plus

the value of (10k-8)(6k+7) when k=12

So you could just do it by calcuating out:

the value of (10k-8)(6k+7) when k=1 is 26

plus

the value of (10k-8)(6k+7) when k=2 is 228

and so on.

It mightn't be a bad idea to do that anyway, since you will understand it thoroughly and be sure of your answer.

However, there are short-cuts.

It may be that you've already covered these in your class, or it may be that you were given this exercise so that you'll appreciate them when you do cover them! :-)

There is a formula for the sum of x from 0 to n and a formula for the sum of x^2 from 0 to n. You can probably find them in your text.

By multiplying out the expression, we can then use those formulas.

- math- Algebra 2 -
**Anonymous**, Sunday, November 1, 2009 at 11:23am
all right great thank you so much!

- math- Algebra 2 -
**jim**, Sunday, November 1, 2009 at 11:39am
You're welcome!

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