Question

Need help on thiss

Answer 1

-28

Answer 2

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

Answer 3

is there a way to put it into wolfram?

Answer 4

I looked at it then I thought of a number.

Answer 5

http://www.wolframalpha.com/input/?i=Sum%5B-2+n+%2B+4%2C+%7Bn%2C+4%2C+7%7D%5D

Answer 6

can you help me with these kind of problems?

Answer 7

Sure.

Answer 8

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

Answer 9

thanks aloot..

Answer 10

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