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CDS 2026 · PYQ · Algebra / LCM-HCF of Polynomials · medium

The LCM and HCF of two polynomials p(x) and q(x) are (x + a)(x³ – a³) and (x² – ax + a²), respectively. If p(x) = x⁴ + a²x² + a⁴, then what is q(x) equal to?

  1. A.x⁴ – 2a²x² + a⁴
  2. B.x⁴ + 2a²x² + a⁴
  3. C.x² – a²✓ Correct
  4. D.x⁴ – a²x² + a⁴

Explanation

Using the relation p(x) × q(x) = LCM × HCF. LCM = (x+a)(x³ – a³) = (x+a)(x–a)(x²+ax+a²) = (x²–a²)(x²+ax+a²). HCF = x² – ax + a². So LCM × HCF = (x²–a²)(x²+ax+a²)(x²–ax+a²) = (x²–a²)(x⁴+a²x²+a⁴). Given p(x) = x⁴ + a²x² + a⁴, so q(x) = LCM × HCF / p(x) = (x²–a²)(x⁴+a²x²+a⁴)/(x⁴+a²x²+a⁴) = x² – a².
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