JMO question---

JMO question---

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2 Answers

Nishant Vora IIT Patna
askIITians Faculty 2467 Points
8 years ago
Hello Student
Please fidn the soln

n6 +3n5_5n4_15n3+4n2+12n+3 =
= n5(n+3) –5n3(n+3)+4n(n+3) + 3
=(n+3)[n5 –5n3+4n] + 3
=n(n+3)[n4-5n2+4] + 3
=n(n+3)(n2-4)(n2-1) + 3
=(n-2)(n-1)n(n+1)(n+2)(n+3) + 3

So this can not be perfect square

mycroft holmes
272 Points
8 years ago
We will prove that this expression is of the form 4k+3 and hence not a perfect square.
 is a multiple of 4. Hence we only need to prove that the following expression is a multiple of 4:
So, we only have to prove that for all n  is divisible by 4.
If n is a multiple of 4, we are done. Else we write the expression as 
We know that if n is not even, then n2-1 is divisible by 4 and hence in this case too the expression is a multiple of 4.
Thus, the polynomial is of the form 4k+3 for all n, and therefore not a perfect square

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