What is the 11th partial sum of #sum_(i=1)^∞ -7i+22#?

Question

1715 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2017-11-29T20:07:39

#-220#

This is an arithmetic series, with first term #15# and common difference #-7#.

The sum of an arithmetic series is:

#n/2(2a+(n-1)d)#

Where, #a# is the first term, #d# is the common difference and #n# is the nth term.

For 11th partial sum:

#11/2[2(15)+(11-1)(-7)]=11/2[30-70]=-220#

#sum_(i=1)^(11)(-7i+22)=-220#