Find the sum of moduli of all roots of:
x^4 - 3x^3 - 2x^2 - 3x +1=0
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The given equation can be written as:-
( x 2 − 4 x + 1 ) ( x 2 + x + 1 ) = 0
Roots of x 2 − 4 x + 1 = 0 are 2 + 3 and 2 − 3
Roots of x 2 + x + 1 = 0 are ω and ω 2 where ω is complex cube root of unity
∣ ω ∣ = ∣ ω 2 ∣ = 1
⇒ Sum of Moduli of roots are:- ( 2 + 3 ) + ( 2 − 3 ) + 1 + 1 = 6