Wednesday 16 December 2015

complex numbers - How to solve $2 - sqrt{3}i + z^{3}=0 $?




I have tried to solve this "problem" so that i have $z$ switched with $a+bi$. Then after some hours of solving this riddle i have gain an enormous numbers of lines but with no solution.



$2 - \sqrt{3}i + z^{3}=0 $



$z=a+bi $



I want to know how much is a and b.


Answer



$z^3=-2+\sqrt{3}i$




Let's express $-2+\sqrt{3}i$ in form of $r(\cos\theta+i\sin\theta)$



$r=\sqrt{4+3}=\sqrt{7}$



$\theta=\arctan(\frac{\sqrt{3}}{2})+\pi$



so we may write that:



$z^3=\sqrt{7}(\cos\theta+i\sin\theta)$




Now if you apply following formula you can calculate $a$ and $b$:



$z=\sqrt [3] {7}(\cos(\frac{\theta+2k\pi}{3})+i\sin(\frac{\theta+2k\pi}{3}))$ ,where $k \in \mathbb{Z}$



so: $a=\sqrt [3] {7}\cos(\frac{\theta+2k\pi}{3})$ and $b=\sqrt [3] {7}\sin(\frac{\theta+2k\pi}{3})$


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