I don't understand how to find a sigma equation from a set of numbers.

-5+2+9+16+...+261+268

How do I get a sigma equation from this?

OfficialBubbleTanks
Feb 23, 2018

#2

#3**+1 **

My answer is the same as EP's

EP you might like to look at my Latex here too :)

-5+2+9+16+...+261+268

This is the sum of an AP

a=-5, d=7,

\(T_n=a+(n-1)d\\ T_n=-5+(n-1)*7\\ T_n=-5+7n-7\\ T_n=7n-12\\ Find\;n\;when\;T_n=268\\ 268=7n-12\\ 280=7n\\ n=40 \)

\(\displaystyle\sum_{n=1}^{40}\;7n-12 \\\)

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LATEX COMMAND

\displaystyle\sum_{n=1}^{40}\;7n-12

Melody
Feb 24, 2018