Aptitude - Numbers - Discussion

Discussion Forum : Numbers - General Questions (Q.No. 3)
3.
It is being given that (232 + 1) is completely divisible by a whole number. Which of the following numbers is completely divisible by this number?
(216 + 1)
(216 - 1)
(7 x 223)
(296 + 1)
Answer: Option
Explanation:

Let 232 = x. Then, (232 + 1) = (x + 1).

Let (x + 1) be completely divisible by the natural number N. Then,

(296 + 1) = [(232)3 + 1] = (x3 + 1) = (x + 1)(x2 - x + 1), which is completely divisible by N, since (x + 1) is divisible by N.

Discussion:
137 comments Page 13 of 14.

Binod Barai said:   7 years ago
2^32+1=2^33.
2^96+1=2^97.
So, it is completely divided.

Supriya Pawar said:   7 years ago
96/3 = 32 so the divisible no is 3.

Kamal said:   6 years ago
Suppose 2^32 = X.
so the first equation is X+1.
we can break 2^96 in 2 ^ 32^3 (mean (2 power 32 )power 3 )
So we can write X^3 + 1 because 2^32 =x already define.

Renu said:   6 years ago
I can't understand the last step. Can anyone help me to get it?

Kavitha said:   6 years ago
Here, the options a,b,c are wrong because all are the smallest value than 2^32 +1.

When you divide a number by largest number, the answer must be decimal so it not whole and not completely divisible. Then final option 2^96 is larger than 2^32. It may be divisible.


Let x= 2^32.
We can write, Power 96=32 *3.
Then 2^96+1=(2^32)^3+1,
We know that (a^3+b^3)=(a+b)(a^2-ab+b^2).
Let a=x i.e,x=2^32.
b=1.

Then
X^3+1=(x+1)(x^2-x+1).
÷by x+1i.e x+1=2^32+1.
Then we get (x^3+1)/(x+1)=x^2-x+1.
And the answer that must be the whole number.
Yes, it is completely divisible by 2^32+1.

Abarna said:   6 years ago
I can't understand it, please explain me.

Tej said:   6 years ago
When we get to handle a big no then just assume for small no;

eg. 2^1(n)+1 always divides 2^3(n)+1;
This pattern followed for all the powers of 2,
For simplest one took n=1
2^1+1=3
2^3+1=9;

For n=2.
2^2+1=5
2^6+1=65;

So we can see the pattern.
Likewise, it follows the last option.

DIYA said:   6 years ago
When it comes to 2^16+1, how can we find its not divisible by n?

(2^8)2+1 = x^2+1=?

Nayudu said:   6 years ago
Agree @Diya.

Can anyone please explain it?

Jyoshna said:   6 years ago
I am not understanding please anyone help me to get it.


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