If x4 + x2y2 + y4 = 126, x2 + xy + y2 = 42, then find x2 - xy + y2 .

Formula → x⁴ + y⁴ + x²y² = (x² + y² + xy) × (x² + y² - xy)

⇒ 126 = 42 × (x² + y² - xy)

⇒ x² + y² - xy = \(\frac{126}{42}\) = 3