1) y⁴ + 4 = (y⁴ + 4y² + 4) - 4y² = [(y²)² + 2 * y² * + 2²] - 4y² = (y² + 2)² - 4y²
2) a⁴ + 2a²b² + 9b⁴ = (a⁴ + 6a²b² + 9b⁴) - 4a²b² = (a² + 3b²)² - 4a²b²
1) y⁴ + 4 = (y⁴ + 4y² + 4) - 4y² = [(y²)² + 2 * y² * + 2²] - 4y² = (y² + 2)² - 4y²
2) a⁴ + 2a²b² + 9b⁴ = (a⁴ + 6a²b² + 9b⁴) - 4a²b² = (a² + 3b²)² - 4a²b²