How many ordered quadruples satisfy where , , are non-zero integers and is a prime?
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Let x , y , z , p be a solution of the above diophantine equation. We can write x as x = ± p m r , where m ≥ 0 is the highest power of p that divides x (This can be zero, if x is not divisible by p ). From the given equation, it is easy to see that p ∣ x 3 , i.e. p ∣ x . So, let x = p x 1 , where x 1 is an integer. Then we have the following equation
p 3 x 1 3 + y 3 p + z 3 p 2 = 0 ,
i.e. y 3 + z 3 p + x 1 3 p 2 = 0
This implies that p ∣ y , So let y = p y 1 , where y 1 is an integer. We have the similar equation again z 3 + x 1 3 p + y 1 3 p 2 = 0 . Thus, p ∣ z . Let z = p z 1 , with z 1 being an integer. Hence we have,
x 1 3 + y 1 3 p + z 1 3 p 2 = 0
Which has the exact same form of the diphantine equation we started with. Hence we can repeat this step more than m + 1 times, to conclude that p m + 1 ∣ x , which contradicts the fact that m is the highest power of p that divides x .
Hence no solution is possible.