Diophantine Inequality 4ax-y^2+z<0

Karley Castillo

Karley Castillo

Answered question

2022-11-13

Diophantine Inequality 4 a x y 2 + z < 0
For fixed positive integer a and positive z in
4 a x y 2 + z < 0 ,
find how many integer solutions (x,y) there are as a function of z Z + , subject to constraints x 0 and a y 0.
This form comes from the quadratic polynomial discriminant. I am not sure where to begin as this isn't the usual quadratic Diophantine inequality (or equation for that matter) that I find through search engines.

Answer & Explanation

Raven Hawkins

Raven Hawkins

Beginner2022-11-14Added 19 answers

Step 1
We can rewrite the starting inequality as x < y 2 z 4 a . Since we also know that x 0, this can be rewritten to
0 x < y 2 z 4 a , 0 y a
Note that y can be further restricted to z < y a. This is because if y z , then the upper bound on x would not be positive.
Step 2
From here, we can go through the possible y and add:
y = z + 1 a y 2 z 4 a
This is the final answer for the number of lattice points in the region.

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