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JAMB Mathematics 1989 Question 22

Question 22

Algebraic Expressions

What are K and L respectively if ½(3y − 4x)2 = (8x2 + Kxy + Ly2)?

  1. A.−12, 9/2
  2. B.−6, 9
  3. C.6, 9
  4. D.12, 9/2.
Show the answer and explanation

Answer: A (−12, 9/2)

Explanation

(3y − 4x)² = 9y² − 24xy + 16x². Half of it is 8x² − 12xy + (9/2)y², so K = −12 and L = 9/2.