Question

Find the sum of the series shown below.

3 + (-6) + (-15) + ... + (-348)

Answer 1

no terms missing, like 9? or 12

Answer 2

Thats if its geometric.

Answer 3

right,,,, o if you add all them together ( even though they are negative ) what is the sum.

Answer 4

what do you mean right...

Answer 5

So is there supposed to be a 9 and 12?

Answer 6

add all the terms from , 3,-6,-15,-24,-33,-42,-51,-60 all the way to -348... whats the sum of that series

Answer 7

could it be arithmetic with common difference -9?

Answer 8

and right means im agreeing with you

Answer 9

Good work cwrw238. I have to go back to class now.

Answer 10

sum = (3-348)39/2

Answer 11

sum n terms = n/2 [ a + l]
but how do we find n?

Answer 12

n = 39

Answer 13

ok since n=39 the equation should be 39{{3+(-348)}
------------
2

Answer 14

348 - 6 = 342
342/9 = 38 + 1 = 39 - oh yes

sum = (39/2) (3 - 348) but that s not a whole number

Answer 15

so in n = 39 correct?

Answer 16

i think its 40
because if we take 3, - 6, - 15 15-6 / 9 = 1 so we need to add 2

Answer 17

so sum = 20 ( 3 - 348) = 20 * -345 = -6900

Answer 18

yep - thats correct devin

Answer 19

i'm convinced of that because if we take say 4 terms

3 -6 -15 - 24
the sum of this is -42

use formula sum = (4/2)*(3 - 24) = 2 * -21 = -42

7 terms :
3,-6,-15,-24,-33,-42,-51
the sum is -168

use formula (7/2)*(3 - 51) = (-48*7 ) / 2 = -168