First slide
Introduction to Determinants
Question

Let α, β, γ are the real roots of the equation x3+ax2+bx+c=0 (a,b,cR and a0). If the system of equations (in u, v and w) given by

αu+βv+γw=0βu+γv+αw=0γu+αv+βw=0

has non-trivial solutions, then the value of a2/b is _______.

Moderate
Solution

Equation x3+ax2+bx+c=0 has roots α, β, γ. Therefore,

α+β+γ=aαβ+βγ+γα=b

Since the given system of equations has non-trivial solutions, we have

αβγβγαγαβ=0

or   α3+β3+γ33αβγ=0or   (α+β+γ)α2+β2+γ2αββγγα=0or   (α+β+γ)(α+β+γ)23(αβ+βγ+γα)=0  aa23b=0or   a2/b=3

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