pinkrose1213
pinkrose1213 pinkrose1213
  • 16-06-2017
  • Mathematics
contestada

Find the 8th term of the geometric sequence if a3=108 and a5=972?

A. 2,268
B. 8,748
C. 26,244
D. 78,732

Respuesta :

LammettHash
LammettHash LammettHash
  • 16-06-2017
[tex]a_3=a_1r^2=108[/tex]
[tex]a_5=a_1r^4=972[/tex]

[tex]\implies\dfrac{a_5}{a_3}=\dfrac{a_1r^4}{a_1r^2}\iff\dfrac{972}{108}=r^2\implies r=\pm\sqrt9=\pm3[/tex]

[tex]a_8=a_1r^7=a_5r^3=972(\pm3)^3[/tex]

Judging by the given choices, the common ratio is likely the positive candidate, so

[tex]a_8=972(3)^3=26244[/tex]

so the answer is C.
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