What is the 6th term of the geometric sequence where a1 = 128 and a3 = 8?

Question

anonymous · Answer

i just need a formula, is all

kamille · Answer

so, whats the problem? Use a formula?

anonymous · Answer

yes, that's what i just asked for..

anonymous · Answer

@nincompoop

kamille · Answer

oh, so you can google it, can't you? http://en.wikipedia.org/wiki/Geometric_progression#Elementary_properties

anonymous · Answer

i didnt understand it which is why I'm here....seeking help

kamille · Answer

So, you know what formula is

$$a ^{n}=a _{1}q ^{n-1}$$

anonymous · Answer

@rajathsbhat 
@Kamille  i don't get the formula is my problem

anonymous · Answer

does this help ? http://www.regentsprep.org/Regents/math/algtrig/ATP2/GeoSeq.htm

anonymous · Answer

the common ratio, how do you find that?

kamille · Answer

oh, it should be $$a _{n}=a _{1}q^{n-1}$$

Well, to get the formula is very easy. Let's say, that there is a number a1 then a2=a1*q, a3=a2*q etc, do you understand why?

anonymous · Answer

$$\Large a_{3}=a_{1}q^{2}$$ right?
you have a3 and a1. Substitute them into the equation to find q. You can then find a6.

kamille · Answer

geometrical progression means that very is a sequance, where 
a1;a2(a1*q);a3(a2*q), etc when q=a2/a1

anonymous · Answer

=0.125

anonymous · Answer

isn't it 0.25 or 1/4?

kamille · Answer

it is 1/4

kamille · Answer

well, why it can't be -1/4?

kamille · Answer

q must be >0?

anonymous · Answer

yep,equally possible

anonymous · Answer

no its 0.125

anonymous · Answer

thanks guys

kamille · Answer

you have forgoten to square root the answer, yummydum

anonymous · Answer

i put 0.125 and it was right...