2a² - b² - (3a - b)²
= 2a² - b² - (9a² - 6ab + b²) (expand the squared term)
= 2a² - b² - 9a² + 6ab - b²
= -7a² + 6ab
Therefore, the simplified expression is -7a² + 6ab.
2a² - b² - (3a - b)²
= 2a² - b² - (9a² - 6ab + b²) (expand the squared term)
= 2a² - b² - 9a² + 6ab - b²
= -7a² + 6ab
Therefore, the simplified expression is -7a² + 6ab.