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Let p,q,r be roots of cubic x^(3)+2X^(2)...

Let `p,q,r` be roots of cubic `x^(3)+2X^(2)+3x+3=0`, then

A

`(p)/(p+1) + (q)/(q+1) + (r )/(r+1) = 5`

B

`((p)/(p+1))^(3) + ((q)/(q+1))^(3) + ((r )/(r+1))^(3) = 45`

C

`((p)/(p+1))+((q)/(q+1))+((r )/(r+1)) = 6`

D

`((p)/(p+1))^(3)+((q)/(q+1))^(3)+((r )/(r+1))^(3)= 46`

Text Solution

Verified by Experts

The correct Answer is:
A

Using transformation, let
`((p)/(p+1)) = y implies p= ((y)/(1-y))`
As,p is root of cubic so
`y^(3)-5y^(2)+6y-3=0`
Now, `y_(1), y_(2),y_(3)` are roots of above equation so
` ((p)/(p+1)+(q)/(q+1)+(r )/(r+1))=5`
Also `Sigmay_(1)=5,Sigmay_(1)y_(2)=6, Sigmay_(1)y_(2)y_(3)=3`
`therefore y_(1)^(3)+y_(2)^(3)+y_(3)^(3)-3y_(1)y _(2)y_(3)`
`= Sigmay_(1)((Sigmay_(1))^(2)-3SigmaY_(1)y_(2))`
`implies y_(1)^(3)+y_(2)^(3)+y_(3)^(3)-3(3)=5((5)^(2)-3(6))`
`impliesy_(1)^(3)+y_(2)^(3)+y_(3)^(3)=44`
` therefore ((p)/(p+1))^(3)+((q)/(q+1))^(3)+((r)/(r+1))^(3)=44`
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