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what is the sum of the first five terms of the geometric sequence if a1 = 3/5 and r = 1/2?
a.5/3
b.9/8
c.93/80
d.72/91​


Sagot :

Answer:

an= a(r)^n-1

r= 1/2

a2= 3/5(1/2)^2-1

a2= 3/5(1/2)¹

a2= 3/5(1/2)

a2= 3/10

a3= 3/5(1/2)^3-1

a3= 3/5(1/2)²

a3= 3/5(1/4)

a3= 3/20

a4= 3/5(1/2)^4-1

a4= 3/5(1/2)³

a4= 3/5(1/8)

a4= 3/40

a5= 3/5(1/2)^5-1

a5= 3/5(1/2)⁴

a5= 3/5(1/16)

a5= 3/80

3/5 + 3/10 + 3/20 + 3/40 + 3/80

3/80 + 3/80 + 3/80 + 3/80 + 3/80

48/80 + 24/80 + 12/80 + 6/80 + 3/80

72/80+ 12/80 + 6/80 + 3/80

84/80 + 6/80 + 3/80

90/80 + 3/80

= 93/80

Answer: C. 93/80