# Geometric Progression

ivanovP
Visitor
2016-04-25 02:29:14
#1
If we have the following geometric progression, (an), with n from N and the properties:
a4 - a2 = 6
a3 - a1 = 3
then a1 and q are:

1) a1 = -1, q = 3
2) a1 = 3, q = 1/2
3) a1 = 2, q = -2
4) a1 =1, q = 2

## RE:Geometric Progression

StefanV
Visitor
2016-04-24 15:00:17
#2
Let's write like this:
a1 = a
a2 = aq
a3 = aq2
a4 = aq3

a4 - a2 = aq3-aq=aq(q2 - 1)
a3 - a1 = a(q2 - 1)

## RE: Geometric Progression

StefanV
Visitor
2016-04-24 15:33:12
#3
$\frac{a_{4}-a_{2}}{a_{3}-a_{1}}=\frac{aq(q^{2}-1)}{a(q^{2}-1)}=q=2$

So, the last option is good

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