Q. Curve \(y^2 = x^6 + 2x^3 + 4x^2 + 4x + 1\).
Answer
To find integer solutions for the curve \(y^2 = x^6 + 2x^3 + 4x^2 + 4x + 1\), compare the polynomial to the perfect square \((x^3 + 1)^2 = x^6 + 2x^3 + 1\).
The equation can be rewritten as:
\[
y^2 = (x^3 + 1)^2 + 4x(x + 1)
\]
For the expression to be a perfect square \(y^2\), the term \(4x(x + 1)\) must satisfy specific conditions.
1. If \(x = 0\), then \(y^2 = (0+1)^2 + 0 = 1\), giving solutions \((0,1)\) and \((0,-1)\).
2. If \(x = -1\), then \(y^2 = (-1+1)^2 + 0 = 0\), giving solution \((-1,0)\).
For other integer values of \(x\), the term \(4x(x + 1)\) is strictly positive, placing \(x^6 + 2x^3 + 4x^2 + 4x + 1\) between consecutive perfect squares for large \(|x|\), which limits further integer solutions.
Final integer solutions \((x,y)\): \((0,1),\ (0,-1),\ (-1,0)\).
Detailed Explanation
Find all integer solutions for the curve \(y^2 = x^6 + 2x^3 + 4x^2 + 4x + 1\)
-
Step 1 – Compare the expression to a known perfect square:
Notice that the first two terms \(x^6 + 2x^3\) are part of the expansion of \((x^3 + 1)^2\). We can expand this square to compare:
\[
(x^3 + 1)^2 = x^6 + 2x^3 + 1.
\]
The difference between the given curve and this square is:
\[
(x^6 + 2x^3 + 4x^2 + 4x + 1) – (x^6 + 2x^3 + 1) = 4x^2 + 4x = 4x(x + 1).
\] -
Step 2 – Identify intervals where the expression lies between squares:
If \(x>0\) or \(x<-1\), the product \(4x(x + 1)\) is strictly positive. This means for these values: \[ y^2 > (x^3 + 1)^2.
\]
Now compare the expression to the next consecutive square, \((x^3 + 2)^2\):
\[
(x^3 + 2)^2 = x^6 + 4x^3 + 4.
\]
Subtracting our expression from this gives:
\[
(x^6 + 4x^3 + 4) – (x^6 + 2x^3 + 4x^2 + 4x + 1) = 2x^3 – 4x^2 – 4x + 3.
\]
For \(x\ge 3\), this difference is positive, meaning
\[
y^2 < (x^3 + 2)^2. \] When an integer \(y^2\) is strictly between two consecutive squares, it cannot be a perfect square itself. -
Step 3 – Test the remaining integer candidates:
Because the bounding logic excludes \(x\ge 3\) and \(x\le -2\), we only need to manually check the integers \(x = -1, 0, 1, 2\).
-
Step 4 – Evaluate \(x = -1\):
\(y^2 = (-1)^6 + 2(-1)^3 + 4(-1)^2 + 4(-1) + 1\)
\(y^2 = 1 – 2 + 4 – 4 + 1 = 0\).
Thus \(y = 0\). This gives the solution \((-1, 0)\).
-
Step 5 – Evaluate \(x = 0\):
\(y^2 = 0^6 + 2\cdot0^3 + 4\cdot0^2 + 4\cdot0 + 1 = 1\).
Thus \(y = \pm 1\). This gives the solutions \((0, 1)\) and \((0, -1)\).
-
Step 6 – Evaluate \(x = 1\) and \(x = 2\):
For \(x = 1\): \(y^2 = 1 + 2 + 4 + 4 + 1 = 12\) (not a square).
For \(x = 2\): \(y^2 = 64 + 16 + 16 + 8 + 1 = 105\) (not a square).
-
Final Answer:
The integer solutions are \((0, 1)\), \((0, -1)\), and \((-1, 0)\).
Graph
FAQs
Can the polynomial in \(y^2 = x^6 + 2x^3 + 4x^2 + 4x + 1\) be factored over \(\mathbb{Q}\) or is it a perfect square?
Is this a hyperelliptic curve and what is its genus?
Are there singular points on the curve?
Does the curve have obvious rational or integer points?
Can this genus-2 curve be parametrized or birationally transformed to an elliptic curve?
How many real components does the real locus have and what is the behavior as \(x\to\pm\infty\)?
What methods can I use to find all rational points on this curve?
How should I visualize or plot the curve \(y^2=f(x)\)?
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