Matrices and Determinants 2 Question 41

45. If α be a repeated root of a quadratic equation f(x)=0 and A(x),B(x) and C(x) be polynomials of degree 3,4 and 5 respectively, then show that

|A(x)B(x)C(x)A(α)B(α)C(α)A(α)B(α)C(α)|

is divisible by f(x), where prime denotes the derivatives.

(1984,3 M)

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Answer:

Solution:

  1. Since, α is repeated root of f(x)=0.

f(x)=a(xα)2,a constant (0)

Let φ(x)=|A(x)B(x)C(x)A(α)B(α)C(α)A(α)B(α)C(α)|

To show φ(x) is divisible by (xα)2, it is sufficient to show that φ(α) and φ(α)=0.

φ(α)=|A(α)B(α)C(α)A(α)B(α)C(α)A(α)B(α)C(α)|=0[R1 and R2 are identical ] Again, φ(x)=|A(x)B(x)C(x)A(α)B(α)C(α)A(α)B(α)C(α)|

=0[R1 and R3 are identical ]

Thus, α is a repeated root of φ(x)=0.

Hence, φ(x) is divisible by f(x).



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