If x4 + x2y2 + y4 = 525, x2 + xy + y2 = 25, then find x2 - xy + y2 .

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

⇒ 525 = 25 × (x² + y² - xy)

⇒ x² + y² - xy = \(\frac{525}{25}\) = 21