Theory of Equations 1 Question 53

54. If α and β are the roots of x2+px+q=0 and γ,δ are the roots of x2+rx+s=0, then evaluate (αγ)(βγ) (αδ)(βδ) in terms of p,q,r and s.

(1979,2M)

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Solution:

  1. Since, α,β are the roots of x2+px+q=0

and γ,δ are the roots of x2+rx+s=0

α+β=p,αβ=q and γ+δ=r,γδ=s

Now, (αγ)(αδ)(βγ)(βδ)

=[α2(γ+δ)α+γδ][β2(γ+δ)β+γδ]=(α2+rα+s)(β2+rβ+s)=(αβ)2+r(α+β)αβ+s(α2+β2)+αβr2+rs(α+β)+s2=q2rqp+s(p22q)+qr2rsp+s2=(qs)2rqprsp+sp2+qr2



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