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JAMB 1990 · UME · Q17

If a2+b2=16a^2 + b^2 = 16 and 2ab=72ab = 7, find all the possible values of (a−b)(a - b).

Worked solution (try it first)
  1. Expand: (a−b)2=a2+b2−2ab(a - b)^2 = a^2 + b^2 - 2ab.
  2. Substitute the given values: (a−b)2=16−7=9(a - b)^2 = 16 - 7 = 9.
  3. A number has two square roots, so a−b=3a - b = 3 or −3-3, option A.

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