Geometric Sequence

Question

What is the sum of the first 6 (starting at n=1) of the geometric sequence with common ratio 7 and a_1=a1=8?

Answer 1

S₆ = [8(1 - (7)⁶] / (1 - 7)

S₆ = [8(1 - 117649)] / -6

S₆ = 8(-117648) / -6

 

Can you calculate from here?

Answer 2

The sum of a geometric sequence of numbers is:  

 

   S_n = [a₁ (1 - rⁿ )] / (1 - r )

 

a₁ is first term of sequence

 

r is common ratio

 

n is number of terms to be summed up

 

     S₆ = [ 8 (1 - 7⁶ )] / ( 1 - 7 )

 

         = -941184/ -6

 

    S_n = 156,864