a3 = -2 (Option E) and a5 = 128 (Option A) are the correct answers.
First lets understand the information mentioned in the question and what we need to find in order to answer the question.
First of all the question tells us that the sequence is a infinite sequence of nonzero integers a(n) = (a(n-1))*(a(n-2))^3 for n>2 terms, and a2 = 2. And then the question asks us to find the value of a3 and a5.
Now lets put the value in the given formula and find out what values we will get.
a3 = (a(3-1))*(a(3-2))^3
[ltr]a3 = (a2)*(a1)^3
a3 = 2*(a1)^3
a4 = (a(4-1))*(a(4-2))^3
a4 = (a3)*(a2)^3, from the question we all know a2 = 2, so (a2)^3 = 8
a4 = 8*(a3)
a4 = 16*(a1)^3
a5 = (a(5-1))*(a(5-2))^3
a5 = (a4)*(a3)^3
a5 = (16*(a1)^3)*(2*(a1)^3)^3
a5 = (16*(a1)^3)*(8*(a1)^9)
a5 = 128*(a1)^12
[/ltr]
From here we know that the key to finding the values of a3 and a5 is to first find the value of a1. But now we don't have any addition information as we have already used all the information which was given in the question. So lets try finding the value of a1 by using the answer options.
So first lets try to find the value of a1 by putting the option values in a3 as it seems easier to solve than solving for a5.
As we call can check from the calculation which we have done till now the value of a5 will be greater than a3. So based on this calculation lets try checking the option from bottom.
First Option E: According to which a3 = -8
2*(a1)^3 = -8
(a1)^3 = -4
From here we can conclude that (-8) is not the right answer to the value of a3 because if we solve any further then a1 will be in decimal form which will defy the condition mention in the question i.e. all the number in series are nonzero integers.
EliminatedNow lets move on to next Option D: a3 = -2
2*(a1)^3 = -2
(a1)^3 = -1
(a1) = -1
This option fits all the condition mentioned in the question. So if we take the value of (a1) to be (-1) then from here a5 will be:
a5 = 128*(a1)^12
a5 = 128*1
a5 =
128 (Option A)After solving this much we have finally got out answers which we were looking for. But lets check other options as well to be double sure.
These steps are just for verifying our option and that's why these are not necessary steps.
Option D: a3 = 4
2*(a1)^3 = 4
(a1)^3 = 2
Eliminated as we will get decimal value from here.
Option C : a3 = 8
(a1)^3 = 4
Eliminated as we will get decimal value from here.
Option B: a3 = 16
(a1)^3 = 8
a1 = 8
Now check for the value of (a5) = 128*(8)^12 and from here only we can understand the value which we will be getting is not even in the option so
Eliminated.Option A: a3 = 128
(a1)^3 = 64
a1 = 4
Again no need to calculate it further here also the value of (a5) = 128*(4)^12 is not in the option so
Eliminated.From here we can finally conclude that a3 = -2 (Option E) and a5 = 128 (Option A) are the only solution available.
Bunuel
The infinite sequence of nonzero integers \(a_1\), \(a_2\), \(a_3\), ... is such that \(a_n = (a_{n-1})(a_{n-2})^3\) for \(n > 2\), and \(a_2 = 2\).
Select for \(a_3\) and \(a_5\) the values of \(a_3\) and \(a_5\), respectively, that would be jointly consistent with the given information. Make only two selections, one in each column.