x^3-9*x^2+27*x-31=0 la ecuación
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Solución
Teorema de Cardano-Vieta
es ecuación cúbica reducida
$$p x^{2} + q x + v + x^{3} = 0$$
donde
$$p = \frac{b}{a}$$
$$p = -9$$
$$q = \frac{c}{a}$$
$$q = 27$$
$$v = \frac{d}{a}$$
$$v = -31$$
Fórmulas de Cardano-Vieta
$$x_{1} + x_{2} + x_{3} = - p$$
$$x_{1} x_{2} + x_{1} x_{3} + x_{2} x_{3} = q$$
$$x_{1} x_{2} x_{3} = v$$
$$x_{1} + x_{2} + x_{3} = 9$$
$$x_{1} x_{2} + x_{1} x_{3} + x_{2} x_{3} = 27$$
$$x_{1} x_{2} x_{3} = -31$$
Suma y producto de raíces
[src]
2/3 2/3 ___ 2/3 2/3 ___
2/3 2 I*2 *\/ 3 2 I*2 *\/ 3
3 + 2 + 3 - ---- - ------------ + 3 - ---- + ------------
2 2 2 2
$$\left(\left(2^{\frac{2}{3}} + 3\right) + \left(- \frac{2^{\frac{2}{3}}}{2} + 3 - \frac{2^{\frac{2}{3}} \sqrt{3} i}{2}\right)\right) + \left(- \frac{2^{\frac{2}{3}}}{2} + 3 + \frac{2^{\frac{2}{3}} \sqrt{3} i}{2}\right)$$
$$9$$
/ 2/3 2/3 ___\ / 2/3 2/3 ___\
/ 2/3\ | 2 I*2 *\/ 3 | | 2 I*2 *\/ 3 |
\3 + 2 /*|3 - ---- - ------------|*|3 - ---- + ------------|
\ 2 2 / \ 2 2 /
$$\left(2^{\frac{2}{3}} + 3\right) \left(- \frac{2^{\frac{2}{3}}}{2} + 3 - \frac{2^{\frac{2}{3}} \sqrt{3} i}{2}\right) \left(- \frac{2^{\frac{2}{3}}}{2} + 3 + \frac{2^{\frac{2}{3}} \sqrt{3} i}{2}\right)$$
$$31$$
$$x_{1} = 2^{\frac{2}{3}} + 3$$
2/3 2/3 ___
2 I*2 *\/ 3
x2 = 3 - ---- - ------------
2 2
$$x_{2} = - \frac{2^{\frac{2}{3}}}{2} + 3 - \frac{2^{\frac{2}{3}} \sqrt{3} i}{2}$$
2/3 2/3 ___
2 I*2 *\/ 3
x3 = 3 - ---- + ------------
2 2
$$x_{3} = - \frac{2^{\frac{2}{3}}}{2} + 3 + \frac{2^{\frac{2}{3}} \sqrt{3} i}{2}$$
x3 = -2^(2/3)/2 + 3 + 2^(2/3)*sqrt(3)*i/2
x1 = 2.2062994740159 + 1.3747296369986*i
x3 = 2.2062994740159 - 1.3747296369986*i
x3 = 2.2062994740159 - 1.3747296369986*i