Problems from Complex numbers from polar to binomic form

Development:

To convert a complex number in polar form into binomial form, we must calculate the coefficients of the real part and the imaginary part of the number. By means of the formula proposed:

$a=13\cdot \cos ({120}^{\circ })=13\cdot (-{\displaystyle \frac{1}{2}})=-{\displaystyle \frac{13}{2}}$

$b=13\cdot \sin ({120}^{\circ })=13\cdot ({\displaystyle \frac{\sqrt{3}}{3}})={\displaystyle \frac{13\cdot \sqrt{3}}{3}}$

This way, $${13}_{{120}^{\circ }}=-{\displaystyle \frac{13}{2}}+{\displaystyle \frac{13\cdot \sqrt{3}}{3}}i$$

Solution:

${13}_{{120}^{\circ }}=-{\displaystyle \frac{13}{2}}+{\displaystyle \frac{13\cdot \sqrt{3}}{3}}i$

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