Q.

Let f(x)=x4+ax3+bx2+c  be a polynomial with real coefficients such that f(1)=9 . Suppose that  i3 is a root of the equation  4x3+3ax2+2bx=0, where i=1 . If α1,α2,α3 and  α4 are all the roots of the equation  f(x)=0,  then  |α1|2+|α2|2+|α3|2+|α4|24  is equal to ……  [|a+ib|=a2+b2  wherea,bR  &1=i]

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answer is 5.

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Detailed Solution

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 f(1)=1+a+b+c=9     a+b+c=10    .....(1)
4x3+3ax2+2bx=0 roots are  3i,3i,0
 4x2+3ax+2b=0<3i3i
 a=0&2b4=(3i)(3i)
b=6 use a, b in (1)  c=16
 f(x)=x4+6x216=0
 (x2+8)(x22)=0
 x=±8i,±2   |α1|2+|α2|2+|α3|2+|α4|24=5

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