Squaring Not Help (maybe..)

Find the number of positive integer solutions (m,n) which satisfy: m + n = 2014 \sqrt{m} + \sqrt{n} = \sqrt{2014} .


The answer is 0.

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2 solutions

Deepansh Mathur
Mar 31, 2014

Okay i think its pretty obvious. If you factor 2014 2014 , it gives 2 , 19 , 53 2,19,53

And none of its factors is a perfect square, all of them are primes. Which implies that there will be 0 0 integral solutions.

Let me explain it with an example. Lets take the number 27 27 in place of 2014 2014 We have m + n = 27 \sqrt{m} + \sqrt{n} = \sqrt{27}

m + n = 9.3 \sqrt{m} + \sqrt{n} = \sqrt{9.3} we can split 27 27 into 9.3 9.3 and here 9 9 is a perfect square

m + n = 3 3 \sqrt{m} + \sqrt{n} = 3 \sqrt{3} \ and now its easy to see that one term on L H S LHS will be 2 3 2 \sqrt{3} and the other will be 3 \sqrt{3}

But this is not possible with 2014 2014 because it has only 3 prime factors, we can't covert their products to same radicals and add them up, its not possible.

Moreover, m m and n n should have the same prime factors because if not, then we can't add them up and receive one single radical.

Garvit Pahal
May 3, 2014

Note that for m,n to be positive integers

m < 2014 m < 2014 and n < 2014 n < 2014

Rearranging the original equation :

m = 2014 n \sqrt{m} = \sqrt{2014} - \sqrt{n}

Squaring we get :

m = 2014 + n 2 2014 n m = 2014 + n - 2*\sqrt{2014*n}

Prime factorization of 2014 = 2 19 53 2014 = 2*19*53 , hence :

m = 2014 + n 2 2 19 53 n m = 2014 + n - 2*\sqrt{2*19*53*n}

Thus for this equation to have positive integral solution , ( 2 19 53 n ) (2*19*53*n) must be a perfect square which is only possible if :

n = 2 19 53 n = 2*19*53

n = 2014 n = 2014

which is not possible as n < 2014 n < 2014 .

Hence the given equation has no solutions.

Note : \textbf{Note :} By the same argument we can show that this kind of an equation ;

m + n = k \sqrt{m} + \sqrt{n} = \sqrt{k}

has no solutions if k does not contain a prime factor with power atleast 2.

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