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JAMB Mathematics 1985 Question 23

Question 23

Linear and Simultaneous Equations

Solve for (x,y) in the equations 2x + y = 4; x2 + xy = −12

  1. A.(6, −8); (−2, 8)
  2. B.(3, −4); (−1, 4)
  3. C.(8, −4); (−1, 4)
  4. D.(−8, 6); (8, −2)
  5. E.(−4, 3); (4, −1)
Show the answer and explanation

Answer: A ((6, −8); (−2, 8))

Explanation

y = 4 − 2x, so x² + x(4 − 2x) = −12, i.e. x² − 4x − 12 = 0 and x = 6 or −2. Then y = −8 or 8.