Problem:
Determine all solutions of the equation
where is a prime number and is an integer.
Problem:
Determine all solutions of the equation
where is a prime number and is an integer.
Solution:
The solutions of the equation are and .
We rewrite the equation in the form
We first observe that for every integer the value of is positive, so all the factors of the equation written above must be positive. We have two cases.
First case: .
For some positive integer we have and . But then , so and . Substituting into the initial equation, one verifies that indeed is a solution.
Second case: . For some positive integer we have and . Substituting the value of given by the second equation into the first equation, we obtain
This last equation has integer solutions if and only if its discriminant
is the square of an integer. This is certainly true if , that is, if . Substituting this value, we obtain and , a solution of the initial equation ( gives no acceptable solutions).
On the other hand, there are no other values of for which is a perfect square. Indeed, it is immediate to see that if then ; in the remaining cases, one has by direct substitution that if then and if then .
Therefore the solutions of the equation are and .