If x4 + x2y2 + y4 = 133, x2 + xy + y2 = 7, then find x2 - xy + y2 .

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

⇒ 133 = 7 × (x² + y² - xy)

⇒ x² + y² - xy = \(\frac{133}{7}\) = 19