2*x^3-6*x+5=0 la ecuación
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Solución
Teorema de Cardano-Vieta
reescribamos la ecuación
$$\left(2 x^{3} - 6 x\right) + 5 = 0$$
de
$$a x^{3} + b x^{2} + c x + d = 0$$
como ecuación cúbica reducida
$$x^{3} + \frac{b x^{2}}{a} + \frac{c x}{a} + \frac{d}{a} = 0$$
$$x^{3} - 3 x + \frac{5}{2} = 0$$
$$p x^{2} + q x + v + x^{3} = 0$$
donde
$$p = \frac{b}{a}$$
$$p = 0$$
$$q = \frac{c}{a}$$
$$q = -3$$
$$v = \frac{d}{a}$$
$$v = \frac{5}{2}$$
Fórmulas de Cardano-Vieta
$$x_{1} + x_{2} + x_{3} = - p$$
$$x_{1} x_{2} + x_{1} x_{3} + x_{2} x_{3} = q$$
$$x_{1} x_{2} x_{3} = v$$
$$x_{1} + x_{2} + x_{3} = 0$$
$$x_{1} x_{2} + x_{1} x_{3} + x_{2} x_{3} = -3$$
$$x_{1} x_{2} x_{3} = \frac{5}{2}$$
2/3
3 ___ 2
x1 = - \/ 2 - ----
2
$$x_{1} = - \sqrt[3]{2} - \frac{2^{\frac{2}{3}}}{2}$$
3 ___ 2/3 / 3 ___ ___ 2/3 ___\
\/ 2 2 | \/ 2 *\/ 3 2 *\/ 3 |
x2 = ----- + ---- + I*|- ----------- + ----------|
2 4 \ 2 4 /
$$x_{2} = \frac{2^{\frac{2}{3}}}{4} + \frac{\sqrt[3]{2}}{2} + i \left(- \frac{\sqrt[3]{2} \sqrt{3}}{2} + \frac{2^{\frac{2}{3}} \sqrt{3}}{4}\right)$$
3 ___ 2/3 /3 ___ ___ 2/3 ___\
\/ 2 2 |\/ 2 *\/ 3 2 *\/ 3 |
x3 = ----- + ---- + I*|----------- - ----------|
2 4 \ 2 4 /
$$x_{3} = \frac{2^{\frac{2}{3}}}{4} + \frac{\sqrt[3]{2}}{2} + i \left(- \frac{2^{\frac{2}{3}} \sqrt{3}}{4} + \frac{\sqrt[3]{2} \sqrt{3}}{2}\right)$$
x3 = 2^(2/3)/4 + 2^(1/3)/2 + i*(-2^(2/3)*sqrt(3)/4 + 2^(1/3)*sqrt(3)/2)
Suma y producto de raíces
[src]
2/3 3 ___ 2/3 / 3 ___ ___ 2/3 ___\ 3 ___ 2/3 /3 ___ ___ 2/3 ___\
3 ___ 2 \/ 2 2 | \/ 2 *\/ 3 2 *\/ 3 | \/ 2 2 |\/ 2 *\/ 3 2 *\/ 3 |
- \/ 2 - ---- + ----- + ---- + I*|- ----------- + ----------| + ----- + ---- + I*|----------- - ----------|
2 2 4 \ 2 4 / 2 4 \ 2 4 /
$$\left(\left(- \sqrt[3]{2} - \frac{2^{\frac{2}{3}}}{2}\right) + \left(\frac{2^{\frac{2}{3}}}{4} + \frac{\sqrt[3]{2}}{2} + i \left(- \frac{\sqrt[3]{2} \sqrt{3}}{2} + \frac{2^{\frac{2}{3}} \sqrt{3}}{4}\right)\right)\right) + \left(\frac{2^{\frac{2}{3}}}{4} + \frac{\sqrt[3]{2}}{2} + i \left(- \frac{2^{\frac{2}{3}} \sqrt{3}}{4} + \frac{\sqrt[3]{2} \sqrt{3}}{2}\right)\right)$$
/3 ___ ___ 2/3 ___\ / 3 ___ ___ 2/3 ___\
|\/ 2 *\/ 3 2 *\/ 3 | | \/ 2 *\/ 3 2 *\/ 3 |
I*|----------- - ----------| + I*|- ----------- + ----------|
\ 2 4 / \ 2 4 /
$$i \left(- \frac{\sqrt[3]{2} \sqrt{3}}{2} + \frac{2^{\frac{2}{3}} \sqrt{3}}{4}\right) + i \left(- \frac{2^{\frac{2}{3}} \sqrt{3}}{4} + \frac{\sqrt[3]{2} \sqrt{3}}{2}\right)$$
/ 2/3\ /3 ___ 2/3 / 3 ___ ___ 2/3 ___\\ /3 ___ 2/3 /3 ___ ___ 2/3 ___\\
| 3 ___ 2 | |\/ 2 2 | \/ 2 *\/ 3 2 *\/ 3 || |\/ 2 2 |\/ 2 *\/ 3 2 *\/ 3 ||
|- \/ 2 - ----|*|----- + ---- + I*|- ----------- + ----------||*|----- + ---- + I*|----------- - ----------||
\ 2 / \ 2 4 \ 2 4 // \ 2 4 \ 2 4 //
$$\left(- \sqrt[3]{2} - \frac{2^{\frac{2}{3}}}{2}\right) \left(\frac{2^{\frac{2}{3}}}{4} + \frac{\sqrt[3]{2}}{2} + i \left(- \frac{\sqrt[3]{2} \sqrt{3}}{2} + \frac{2^{\frac{2}{3}} \sqrt{3}}{4}\right)\right) \left(\frac{2^{\frac{2}{3}}}{4} + \frac{\sqrt[3]{2}}{2} + i \left(- \frac{2^{\frac{2}{3}} \sqrt{3}}{4} + \frac{\sqrt[3]{2} \sqrt{3}}{2}\right)\right)$$
$$- \frac{5}{2}$$
x1 = 1.02681078793949 - 0.40375881747242*i
x2 = 1.02681078793949 + 0.40375881747242*i