## anonymous 4 years ago Need help on thiss

1. anonymous

2. anonymous

-28

3. anonymous

how did you solve it...i have 5 more problems like this..

4. anonymous

is there a way to put it into wolfram?

5. anonymous

I looked at it then I thought of a number.

6. anonymous
7. anonymous

can you help me with these kind of problems?

8. anonymous

Sure.

9. anonymous

Given the sequence 9, 12, 15, which of the following is equivalent to

10. anonymous

thanks aloot..

11. mathmate

You can split the summations, and evaluate each one separately. $\sum_{4}^{7}-2n+4 = \sum_{4}^{7}-2n + \sum_{4}^{7}4$ $= -2\sum_{4}^{7}n + 4\sum_{4}^{7} 1$ $= -2(\sum_{1}^{7}n - \sum_{1}^{3}n ) + 4(4)$ $= -2[ 7(7+1)/2 - 3(3+1)/2 ] - 16$ $= -44 + 16$ $= -28$