Find the sum of the first 12 terms of the sequence. Show all work for full credit.

1, -4, -9, -14, . . .

Question

Find the sum of the first 12 terms of the sequence. Show all work for full credit.

1, -4, -9, -14, . . .

chihiroasleaf · Answer

this is arithmetic sequence, 
the sum of the n first term is 
$$Sn = \frac{ n }{ 2 }\left( 2a + \left( n-1 \right)  d \right)$$
with
 n = the number of terms
a = the first term 
d = the difference

you can use this formula to solve the problem
can you determine, what is n, a, and d of your sequence?

anonymous · Answer

d=-9-(-4)
  =-9+4
  =-5
n=12
a=1.

chihiroasleaf · Answer

yess... :)
now, plug in the value into the formula...

anonymous · Answer

12/2(2*1+(12-1)-5)

anonymous · Answer

which equals 48?

chihiroasleaf · Answer

be careful in calculation.... :)|dw:1354117455248:dw|