A sequence has a common ratio

Question

A sequence has a common ratio of R=-2 so if G₃=7 what is G₅? 

 

A. 3 

B. -14 

C. 28 

D. -28

Answer 1

C(-2^0) = C  <---G1

 

C(-2^1) = -2C <--- G2

 

C(-2)^3 = 7 <--- G3

 

-8C = 7

 

C = -7/8

 

So G5 = (-7/8)(-2)^4 = (-7/8)(16) = -14

 

G(n) = (-7/8)(-2)^(n-1)

 

Answer : B

Answer 2

G_n = G₁r^n-1

 

G₃ = G₁(-2)² = 7

 

So, G₁ = 7/4

 

G₅ = G₁r⁴ = (7/4)(-2)⁴ = 28

 

Answer:  C