(x² - y²)² + (2xy)² = (x² + y²)²
(x² - y²)(x² - y²) + 2x²y² = (x² + y²)(x² + y²)
x²(x² - y²) - y²(x² - y²) + 2x²y² = x²(x² + y²) + y²(x² + y²)
x²(x²) - x²(y²) - y²(x²) + y²(y²) + 2x²y² = x²(x²) + x²(y²) + y²(x²) + y²(y²)
x⁴ - x²y² - x²y² + y⁴ + 2x²y² = x⁴ + x²y² + x²y² + y⁴
x⁴ - 2x²y² + y⁴ + 2x²y² = x⁴ + 2x²y² + y⁴
x⁴ - 2x²y² + 2x²y² + y⁴ = x⁴ + 2x²y² + y⁴
x⁴ + y⁴ = x⁴ + 2x²y² + y⁴
- x⁴ - x⁴
y⁴ = 2x²y² + y⁴
- y⁴ - y⁴
0 = 2x²y²
2 2
0 = x²y²
0 = xy
I didn't find the answer to the problem.