1) (x-y)² + (x+y)² = x² - 2xy + y² + x² + 2xy + y² = 2x² + 2y² = 2(x² + y²)
2) (a-2b)² + 4b(a+b) = a² - 4ab + 4b² + 4ab + 4b² = a² + 8b²
3) (6+x²)² - (8-x²)² + 28 = 36 + 12x² + x⁴ - 64 + 16x² - x⁴ + 28 = 28 + 28x²
4) (4-5x³)² - (3+5x³)(5x³-3) = 16 - 40x³ + 25x^6 - 15x³ - 15x^6 + 9 = -30x³ + 25x^6 + 9 = 5(5 - 8x³)
1) (x-y)² + (x+y)² = x² - 2xy + y² + x² + 2xy + y² = 2x² + 2y² = 2(x² + y²)
2) (a-2b)² + 4b(a+b) = a² - 4ab + 4b² + 4ab + 4b² = a² + 8b²
3) (6+x²)² - (8-x²)² + 28 = 36 + 12x² + x⁴ - 64 + 16x² - x⁴ + 28 = 28 + 28x²
4) (4-5x³)² - (3+5x³)(5x³-3) = 16 - 40x³ + 25x^6 - 15x³ - 15x^6 + 9 = -30x³ + 25x^6 + 9 = 5(5 - 8x³)