Question

given the geometric sequence with $a_4 = 80$ and $a_5 = 160$, write down the first three terms.
select one:
a. \\{10,20,40\\}
b. \\{5,10,20\\}
c. \\{640,320,160\\}
d. \\{2,4,8\\}

Explanation:

Step1: Find common ratio $r$

$r = \frac{a_5}{a_4} = \frac{160}{80} = 2$

Step2: Find $a_3$ using $a_4$

$a_3 = \frac{a_4}{r} = \frac{80}{2} = 40$

Step3: Find $a_2$ using $a_3$

$a_2 = \frac{a_3}{r} = \frac{40}{2} = 20$

Step4: Find $a_1$ using $a_2$

$a_1 = \frac{a_2}{r} = \frac{20}{2} = 10$

Answer:

A. {10,20,40}