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JAMB 1985 · UME · Q21

If the quadratic function 3x2−7x+R3x^2 - 7x + R is a perfect square, find RR.

Worked solution (try it first)
  1. A quadratic is a perfect square when it has equal roots, so b2=4acb^2 = 4ac.
  2. Here a=3a = 3, b=−7b = -7 and c=Rc = R: 49=4×3×R=12R49 = 4 \times 3 \times R = 12R.
  3. So R=4912R = \frac{49}{12}, option D.

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