Unknown coefficients of a cubic with a quadratic factor, its roots and a remainder

Unknown coefficients of a cubic with a quadratic factor, its roots and a remainder

7 marks

The cubic polynomial \(\mathrm{P}(x)=px^3+qx^2-13x-6\), where \(p\) and \(q\) are constants, has \(x^2-x-6\) as a factor.

  1. Find the value of \(p\) and the value of \(q\).[4]
  2. Find all three roots of the equation \(\mathrm{P}(x)=0\).[2]
  3. Find the remainder when \(\mathrm{P}(x)\) is divided by \(x-2\).[1]

Solution:

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Answer:(a) \(p=2,\ q=-1\) (b) \(x=3,\ -2,\ -\frac12\) (c) \(-20\)

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