For the sequence -3, -12, -48, … how do you find the sum of the first 12 terms?

1 Answer
Mar 7, 2016

Answer:

Use the formula #sum_0^n = (a(1-r^n))/(1-r)# where #a# is the first term, #r# is the common ratio and #n# is the number of terms.

Explanation:

The sequence here is #-3, (-3*4), (-3*4*4),......#

So the #n#th term is #(-3)*4^(n-1)#

The first term is #-3# and the common ratio is #4#.

#sum_1^12 = ((-3)(1-4^12))/(1-4) =((-3)(-16777215))/(-3)#

#=-16777215#