anonymous
  • anonymous
Find the sum of the first 12 terms of the sequence. Show all work for full credit. 1, -4, -9, -14, . . . please this is my last question and i cant seem to get it right. if possible can someone work it out for me?
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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katieb
  • katieb
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campbell_st
  • campbell_st
what do you know about the question..?
anonymous
  • anonymous
i believe its an arithmetic sequence?
campbell_st
  • campbell_st
good start, what's the common difference..?

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anonymous
  • anonymous
ok that where i confuse myself
campbell_st
  • campbell_st
well what is the sequence changing by... common difference = 2nd term - 1st term check with 3rd term - 2nd term.... is it the same
anonymous
  • anonymous
-5
campbell_st
  • campbell_st
great... and the 1st term a = 1 so for the sum of the sequence you can use the formula \[S_{n} = \frac{n}{2}[2a + (n - 1) \times d]\] you are given a = 1, you found d = -5 and have been told n = 12 so substitute them and calculate the sum
anonymous
  • anonymous
i get the plugging in but what does d equal? all the rest i plugged in
campbell_st
  • campbell_st
d is the common difference d = -5
anonymous
  • anonymous
i see ok 1 min
anonymous
  • anonymous
is it 6/-53
anonymous
  • anonymous
that's what i got but I not entirely sure.
campbell_st
  • campbell_st
you are close the calculation becomes \[S_{12} = \frac{12}{2} \times (-53)\]
campbell_st
  • campbell_st
so then \[S_{12} = 6 \times (-53)\]
anonymous
  • anonymous
so that is the final form?

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