Find the sum of the series.
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Question

anonymous · Answer

attachment

anonymous · Answer

This is arithmetic series, so use arithmetic formula

anonymous · Answer

really?  i guess so but i don't know it.  i would take 
$$96\sum_{k=1}^{20} 1-12\sum_{k=1}^{20}k$$

anonymous · Answer

then subtract off first two. first one is obviously 
$$20\times 96$$

anonymous · Answer

second one is 
$$-12\frac{20(21)}{2}$$

saifoo.khan · Answer

http://openstudy.com/groups/mathematics#/groups/mathematics/updates/4e24e5f00b8b3d38d3b7622b Help

saifoo.khan · Answer

just for a sec!

saifoo.khan · Answer

Just chk where i went wrong!

saifoo.khan · Answer

Simplest ques ever!

anonymous · Answer

i get -600 from which i have to subtract 
$$96-12+(96-24)=180$$

anonymous · Answer

i get -780

anonymous · Answer

THANKS EVERYONE

anonymous · Answer

k doesn't equal 1, it equals 3 in the attached equation. Answer should be -756. I'll post the equations in a min.

anonymous · Answer

i know k = 3 that is why i subtracted off the first two terms.  could be arithmetic mistake though

anonymous · Answer

In that equation, you're doing:
(96x20) - 12 [20*21/2]
1920 - 2520 = -600

Now 96−12+(96−24) doesn't equal 180, it equals 156 (didn't subtract the 24)

-600 - 156 = -756

Always double check your work :) I got to the same answer by a more complicated usage of summation, but at least now we're sure it's right and we know WHY :)