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Question

If the product of two roots of the equation x45x3+5x2+5x6=0 is 3, then which of the following is/are correct?

A
The product of all negative roots will be 6.
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B
The equation has only one negative root.
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C
The product of all positive roots will be 6.
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D
The equation has three negative roots.
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Solution

The correct option is C The product of all positive roots will be 6.
Let α,β,γ,δ be the roots of the equation given, so
s1=α+β+γ+δ=5
s2=αβ+αγ+αδ+βγ+βδ+γδ=5
s3=αβγ+αβδ+γδα+γδβ=5
s4=αβγδ=6

Assuming αβ=3 then from s4
γδ=2
Now from s3, we get
3(γ+δ)2(α+β)=5
From s1
(γ+δ)+(α+β)=5
Solving these two equations on α+β,γ+δ, we get
α+β=4, γ+δ=1

Now,
α+β=4,αβ=3 and γ+δ=1,γδ=2

Solving them, we get
α=3,β=1 or α=1,β=3
γ=2,δ=1 or γ=1,δ=2

Therefore, the roots of the given equation are 1,1,2,3.

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