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QJEEAdv24Ma6ce2: JEE Advanced 2024 Mathematics - Class 11 JEEAdv24Ma6ce2 Solution: Let be a polynomial with real coefficients such that . Suppose…

Let f(x)=x4+ax3+bx2+cf(x)=x^4+a x^3+b x^2+c be a polynomial with real coefficients such that f(1)=−9f(1)=-9 . Suppose that i3i \sqrt{3} is a root of the equation 4x3+3ax2+2bx=04 x^3+3 a x^2+2 b x=0 , where i=−1i=\sqrt{-1} . If α1,α2,α3\alpha_1, \alpha_2, \alpha_3 , and α4\alpha_4 are all the roots of the equation f(x)=0f(x)=0 , then ∣α1∣2+∣α2∣2+∣α3∣2+∣α4∣2\left|\alpha_1\right|^2+\left|\alpha_2\right|^2+\left|\alpha_3\right|^2+\left|\alpha_4\right|^2 is equal to ____________.

Step-by-Step Verified Solution

f(1)=1+a+b+c=−9⇒a+b+c=−10.... (i)f(1)=1+a+b+c=-9 \quad \Rightarrow \quad a+b+c=-10\quad \text{.... (i)}

amp;4x3+3ax2+2bx=0 roots are 3i,−3i,0amp;⇒4x2+3ax+2 b=0lt;3i−3iamp;⇒a=0&2 b4=(3i)(−3i)amp;b=6 use a,b in (1) ⇒c=−16amp;⇒f(x)=x4+6x216=0amp;(x2+8)(x2−2)=0amp;⇒x=±8i,±2⇒∣α1∣2+∣α2∣2+∣α3∣2+∣α4∣2=20amp;\begin{aligned}& 4 x^3+3 a x^2+2 b x=0 \text { roots are } \sqrt{3} i,-\sqrt{3} i, 0 \\& \Rightarrow \quad 4 \mathrm{x}^2+3 \mathrm{ax}+2 \mathrm{~b}=0<\begin{array}{l}\sqrt{3} i \\-\sqrt{3} i\end{array} \\& \Rightarrow \quad \mathrm{a}=0 \& \frac{2 \mathrm{~b}}{4}=(\sqrt{3} \mathrm{i})(-\sqrt{3} \mathrm{i}) \\& \mathrm{b}=6 \text { use } \mathrm{a}, \mathrm{b} \text { in (1) } \Rightarrow \mathrm{c}=-16 \\& \Rightarrow \quad \mathrm{f}(\mathrm{x})=\mathrm{x}^4+6 \mathrm{x}^2 \quad 16=0 \\& \left(x^2+8\right)\left(x^2-2\right)=0 \\& \Rightarrow \quad \mathrm{x}= \pm \sqrt{8} \mathrm{i}, \pm \sqrt{2} \quad \Rightarrow \quad\left|\alpha_1\right|^2+\left|\alpha_2\right|^2+\left|\alpha_3\right|^2+\left|\alpha_4\right|^2=20 \\&\end{aligned}

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