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 5 of 14.

Shreya said:   7 years ago
Hi;

Actually, if any no is of the form a^n +b^n if n is odd.

So, here if in 2^96 + 1 we take n=3 it will become (2^32)^3 + (1^32)^3..to tell you we took n=3 so that we get 32 after dividing...now from the above-mentioned formula (2^32)^3 + (1^32)^3 will always be divisible by 2^32 + 1^32 as n is odd.
Therefore 2^32 + 1 completely divides 2^96 + 1.

Akriti said:   7 years ago
I can't understand last step how it will completely divisible?

Please explain again in simple step.

Priya DP said:   8 years ago
By trial and error method only option A&D are applicable

Yuvraj said:   8 years ago
I Can't understand, how to solve this? Someone help me.

Yuvraj said:   8 years ago
I can't understand to which way solve this question please explain in simple way.

Karna said:   8 years ago
Here, We know that (x^n+y^n) is divisible by (x+a) for natural numbers.

Shyam said:   8 years ago
Let 2^32 be x.
2^32+1 = x+1----------->(1)
2^96+1 = (2^32)^3+1
= x^3+1
= (x+1)(x^2-x+1)--------->(2)

By (2)÷(1)
2^96+1/2^32+1 = (x+1)(x^2-x+1)/(x+1).
= x^2-x+1.

So, 2^96+1 Is completely divisible by 2^32+1.

Lupu gogoi said:   8 years ago
We are finding the answer. We don't know what is the answer above this problem. Then how to you directly put the answer 2^96+1.

How you know the answer is that? If the problem given you another then how to you solve that. Please explain.

Aravinth Kumar said:   8 years ago
@Kishore Sulthana.

Good explanation. I can understand it now.

Kranthi said:   8 years ago
Remember the condition that (x^n+1^n) is divisible by (x+1). Given number (2^32+1) is divisor. He said which of the following number is divided by this number i.e. (2^32+1). The dividend should be in the form of (x^n+1^n). Let x=2^32(from divisor).

Substituae it in dividend. [(2^32)^n+1^n].

Substitube n= 1,3,5,... 4 th option suits when n=3.


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