Question

Determine the common ratio r of a geometric sequence with first term 5 and fourth term
-40.​

Answer 1

Answer:

r = -2

Step-by-step explanation:

a1 = 5

a4 = -40

Let terms of GP be  $a , ar, ar^{2} , ar^{3}$ with common ratio r.

Now

$a1 = a = 5$

$a4 = ar^{3} = -40$

$ar^{3} / a = -40 / 5$

$ar^{3} / a = -8$

$r^{3} = -8$

$r = \sqrt[3]{-8}$

$r = -2$