Question

What is the sum of the geometric sequence –1, 6, –36, … if there are 7 terms?

Answer 1

here, common ratio (r)= 6/-1=-6
and first term (a1)=-1
no of terms(n)=7
so,
sum = a1(r^n-1)/(r-1)
apply this and find the answer

Answer 2

\[S_{n} = \frac{a_{1}(1 - r^{n})}{1 - r}\]

Answer 3

Where n = 7 and a_1 = -1

Answer 4

the common ratio r = -6 n = 7 and a = -1

\[S _{7} = \frac{-1( (-6)^7 -1)}{-6 -1}\]

Answer 5

sum =-39991

Answer 6

thanks!!

Answer 7

yes thats it