Saturday, 14 November 2015

complex numbers - Roots of polynomial with imaginary coefficients



This is the first time I see this kind of problem, so it might be trivial but I am just not used to it.




What are the roots of $x^3-6ix^2-11x+6i$



I am not sure If I should ignore the imaginary numbers and simply compute the polynomial or factor the imaginary part out separately.



I tried to use the rational polynomial root test but it has no rational roots when I ignore the Imaginary coefficients.



When I factor them out as $x^3-11x-i(6x^2-6)$ I get $i$ and $-i$ as a root which is definitely wrong.



All I ask for here is to provide me advice on what method should I use to solve this type of problems. Thanks in advance.


Answer




Hint:



$x=iy$



Now if $f(y)=y^3-6y^2+11y-6$



$f(1)=?$


No comments:

Post a Comment

real analysis - How to find $lim_{hrightarrow 0}frac{sin(ha)}{h}$

How to find $\lim_{h\rightarrow 0}\frac{\sin(ha)}{h}$ without lhopital rule? I know when I use lhopital I easy get $$ \lim_{h\rightarrow 0}...