Question

find the sum of first 8 terms of the GP 1 3 9 27 81​

Answer 1

Answer:

Step-by-step explanation:

as we know that sum of GP=a(r^n -1)/r-1

therefore,here n=8

a=1

ar=3

therefore,r = ar-a

                 r=3-1

                 r=2

now by substituting in sum equation,

we get

s8=1(2^8 -1)/2-1

s8=256-1/1

therefore,sum of first 8 terms equals to 255

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Answer 2

first term (a) = 1

common ratio (r) = 3/1 = 3

sum of first 8 terms =?

Since

S,n = a(r^n-1)/r-1

S,8 = 1(3^8- 1))/(3-1)

= (6561-1)/2

= 6560/2= 3280------ANS