Q21 of 25 Page 2

Obtain all zeros of the polynomial f(x) = 2x4 + x3 – 14x2 –19x – 6, if two of its zeros are –2 and –1.

We know that if (x – a) is a zero of a polynomial then (x – a) is a factor of f(x)


Since –2 and –1 are zeros of f(x).Therefore, (x + 2)(x + 1) = x2 + 3x + 2 is a factor of f(x).


Now on dividing f(x) = 2x4 + x3 – 14x2 –19x – 6 by g(x) = x2 + 3x + 2 to find other zeros.



By applying division algorithm, we have:


2x4 + x3 – 14x2 –19x – 6 = (x2 + 3x + 2)(2x2 – 5x – 3)


2x4 + x3 – 14x2 –19x – 6 = (x + 2)(x + 1)(2x2 – 5x – 3)


2x4 + x3 – 14x2 –19x – 6 = (x + 2)(x + 1)(2x + 1)(x – 3)


Hence, the zeros of the given polynomial are –1/2, –1, –2, 3.


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