## whatevs Need help on thiss 2 years ago 2 years ago

1. whatevs

2. FoolForMath

-28

3. whatevs

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

4. whatevs

is there a way to put it into wolfram?

5. FoolForMath

I looked at it then I thought of a number.

6. FoolForMath
7. whatevs

can you help me with these kind of problems?

8. FoolForMath

Sure.

9. whatevs

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

10. whatevs

thanks aloot..

11. mathmate

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