x^4-3x^2+4=0 la ecuación
El profesor se sorprenderá mucho al ver tu solución correcta😉
Solución
Solución detallada
Tenemos la ecuación:
( x 4 − 3 x 2 ) + 4 = 0 \left(x^{4} - 3 x^{2}\right) + 4 = 0 ( x 4 − 3 x 2 ) + 4 = 0 Sustituimos
v = x 2 v = x^{2} v = x 2 entonces la ecuación será así:
v 2 − 3 v + 4 = 0 v^{2} - 3 v + 4 = 0 v 2 − 3 v + 4 = 0 Es la ecuación de la forma
a*v^2 + b*v + c = 0 La ecuación cuadrática puede ser resuelta
con la ayuda del discriminante.
Las raíces de la ecuación cuadrática:
v 1 = D − b 2 a v_{1} = \frac{\sqrt{D} - b}{2 a} v 1 = 2 a D − b v 2 = − D − b 2 a v_{2} = \frac{- \sqrt{D} - b}{2 a} v 2 = 2 a − D − b donde D = b^2 - 4*a*c es el discriminante.
Como
a = 1 a = 1 a = 1 b = − 3 b = -3 b = − 3 c = 4 c = 4 c = 4 , entonces
D = b^2 - 4 * a * c = (-3)^2 - 4 * (1) * (4) = -7 Como D < 0 la ecuación
no tiene raíces reales,
pero hay raíces complejas.
v1 = (-b + sqrt(D)) / (2*a) v2 = (-b - sqrt(D)) / (2*a) o
v 1 = 3 2 + 7 i 2 v_{1} = \frac{3}{2} + \frac{\sqrt{7} i}{2} v 1 = 2 3 + 2 7 i v 2 = 3 2 − 7 i 2 v_{2} = \frac{3}{2} - \frac{\sqrt{7} i}{2} v 2 = 2 3 − 2 7 i Entonces la respuesta definitiva es:
Como
v = x 2 v = x^{2} v = x 2 entonces
x 1 = v 1 x_{1} = \sqrt{v_{1}} x 1 = v 1 x 2 = − v 1 x_{2} = - \sqrt{v_{1}} x 2 = − v 1 x 3 = v 2 x_{3} = \sqrt{v_{2}} x 3 = v 2 x 4 = − v 2 x_{4} = - \sqrt{v_{2}} x 4 = − v 2 entonces:
x 1 = x_{1} = x 1 = 0 1 + ( 3 2 + 7 i 2 ) 1 2 1 = 3 2 + 7 i 2 \frac{0}{1} + \frac{\left(\frac{3}{2} + \frac{\sqrt{7} i}{2}\right)^{\frac{1}{2}}}{1} = \sqrt{\frac{3}{2} + \frac{\sqrt{7} i}{2}} 1 0 + 1 ( 2 3 + 2 7 i ) 2 1 = 2 3 + 2 7 i x 2 = x_{2} = x 2 = 0 1 + ( − 1 ) ( 3 2 + 7 i 2 ) 1 2 1 = − 3 2 + 7 i 2 \frac{0}{1} + \frac{\left(-1\right) \left(\frac{3}{2} + \frac{\sqrt{7} i}{2}\right)^{\frac{1}{2}}}{1} = - \sqrt{\frac{3}{2} + \frac{\sqrt{7} i}{2}} 1 0 + 1 ( − 1 ) ( 2 3 + 2 7 i ) 2 1 = − 2 3 + 2 7 i x 3 = x_{3} = x 3 = 0 1 + ( 3 2 − 7 i 2 ) 1 2 1 = 3 2 − 7 i 2 \frac{0}{1} + \frac{\left(\frac{3}{2} - \frac{\sqrt{7} i}{2}\right)^{\frac{1}{2}}}{1} = \sqrt{\frac{3}{2} - \frac{\sqrt{7} i}{2}} 1 0 + 1 ( 2 3 − 2 7 i ) 2 1 = 2 3 − 2 7 i x 4 = x_{4} = x 4 = 0 1 + ( − 1 ) ( 3 2 − 7 i 2 ) 1 2 1 = − 3 2 − 7 i 2 \frac{0}{1} + \frac{\left(-1\right) \left(\frac{3}{2} - \frac{\sqrt{7} i}{2}\right)^{\frac{1}{2}}}{1} = - \sqrt{\frac{3}{2} - \frac{\sqrt{7} i}{2}} 1 0 + 1 ( − 1 ) ( 2 3 − 2 7 i ) 2 1 = − 2 3 − 2 7 i
Gráfica
-3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0 20
/ / ___\\ / / ___\\
| |\/ 7 || | |\/ 7 ||
|atan|-----|| |atan|-----||
___ | \ 3 /| ___ | \ 3 /|
x1 = - \/ 2 *cos|-----------| - I*\/ 2 *sin|-----------|
\ 2 / \ 2 /
x 1 = − 2 cos ( atan ( 7 3 ) 2 ) − 2 i sin ( atan ( 7 3 ) 2 ) x_{1} = - \sqrt{2} \cos{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)} - \sqrt{2} i \sin{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)} x 1 = − 2 cos 2 atan ( 3 7 ) − 2 i sin 2 atan ( 3 7 )
/ / ___\\ / / ___\\
| |\/ 7 || | |\/ 7 ||
|atan|-----|| |atan|-----||
___ | \ 3 /| ___ | \ 3 /|
x2 = - \/ 2 *cos|-----------| + I*\/ 2 *sin|-----------|
\ 2 / \ 2 /
x 2 = − 2 cos ( atan ( 7 3 ) 2 ) + 2 i sin ( atan ( 7 3 ) 2 ) x_{2} = - \sqrt{2} \cos{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)} + \sqrt{2} i \sin{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)} x 2 = − 2 cos 2 atan ( 3 7 ) + 2 i sin 2 atan ( 3 7 )
/ / ___\\ / / ___\\
| |\/ 7 || | |\/ 7 ||
|atan|-----|| |atan|-----||
___ | \ 3 /| ___ | \ 3 /|
x3 = \/ 2 *cos|-----------| - I*\/ 2 *sin|-----------|
\ 2 / \ 2 /
x 3 = 2 cos ( atan ( 7 3 ) 2 ) − 2 i sin ( atan ( 7 3 ) 2 ) x_{3} = \sqrt{2} \cos{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)} - \sqrt{2} i \sin{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)} x 3 = 2 cos 2 atan ( 3 7 ) − 2 i sin 2 atan ( 3 7 )
/ / ___\\ / / ___\\
| |\/ 7 || | |\/ 7 ||
|atan|-----|| |atan|-----||
___ | \ 3 /| ___ | \ 3 /|
x4 = \/ 2 *cos|-----------| + I*\/ 2 *sin|-----------|
\ 2 / \ 2 /
x 4 = 2 cos ( atan ( 7 3 ) 2 ) + 2 i sin ( atan ( 7 3 ) 2 ) x_{4} = \sqrt{2} \cos{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)} + \sqrt{2} i \sin{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)} x 4 = 2 cos 2 atan ( 3 7 ) + 2 i sin 2 atan ( 3 7 )
x4 = sqrt(2)*cos(atan(sqrt(7)/3)/2) + sqrt(2)*i*sin(atan(sqrt(7)/3)/2)
Suma y producto de raíces
[src]
/ / ___\\ / / ___\\ / / ___\\ / / ___\\ / / ___\\ / / ___\\ / / ___\\ / / ___\\
| |\/ 7 || | |\/ 7 || | |\/ 7 || | |\/ 7 || | |\/ 7 || | |\/ 7 || | |\/ 7 || | |\/ 7 ||
|atan|-----|| |atan|-----|| |atan|-----|| |atan|-----|| |atan|-----|| |atan|-----|| |atan|-----|| |atan|-----||
___ | \ 3 /| ___ | \ 3 /| ___ | \ 3 /| ___ | \ 3 /| ___ | \ 3 /| ___ | \ 3 /| ___ | \ 3 /| ___ | \ 3 /|
- \/ 2 *cos|-----------| - I*\/ 2 *sin|-----------| + - \/ 2 *cos|-----------| + I*\/ 2 *sin|-----------| + \/ 2 *cos|-----------| - I*\/ 2 *sin|-----------| + \/ 2 *cos|-----------| + I*\/ 2 *sin|-----------|
\ 2 / \ 2 / \ 2 / \ 2 / \ 2 / \ 2 / \ 2 / \ 2 /
( ( 2 cos ( atan ( 7 3 ) 2 ) − 2 i sin ( atan ( 7 3 ) 2 ) ) + ( ( − 2 cos ( atan ( 7 3 ) 2 ) − 2 i sin ( atan ( 7 3 ) 2 ) ) + ( − 2 cos ( atan ( 7 3 ) 2 ) + 2 i sin ( atan ( 7 3 ) 2 ) ) ) ) + ( 2 cos ( atan ( 7 3 ) 2 ) + 2 i sin ( atan ( 7 3 ) 2 ) ) \left(\left(\sqrt{2} \cos{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)} - \sqrt{2} i \sin{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)}\right) + \left(\left(- \sqrt{2} \cos{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)} - \sqrt{2} i \sin{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)}\right) + \left(- \sqrt{2} \cos{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)} + \sqrt{2} i \sin{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)}\right)\right)\right) + \left(\sqrt{2} \cos{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)} + \sqrt{2} i \sin{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)}\right) 2 cos 2 atan ( 3 7 ) − 2 i sin 2 atan ( 3 7 ) + − 2 cos 2 atan ( 3 7 ) − 2 i sin 2 atan ( 3 7 ) + − 2 cos 2 atan ( 3 7 ) + 2 i sin 2 atan ( 3 7 ) + 2 cos 2 atan ( 3 7 ) + 2 i sin 2 atan ( 3 7 )
/ / / ___\\ / / ___\\\ / / / ___\\ / / ___\\\ / / / ___\\ / / ___\\\ / / / ___\\ / / ___\\\
| | |\/ 7 || | |\/ 7 ||| | | |\/ 7 || | |\/ 7 ||| | | |\/ 7 || | |\/ 7 ||| | | |\/ 7 || | |\/ 7 |||
| |atan|-----|| |atan|-----||| | |atan|-----|| |atan|-----||| | |atan|-----|| |atan|-----||| | |atan|-----|| |atan|-----|||
| ___ | \ 3 /| ___ | \ 3 /|| | ___ | \ 3 /| ___ | \ 3 /|| | ___ | \ 3 /| ___ | \ 3 /|| | ___ | \ 3 /| ___ | \ 3 /||
|- \/ 2 *cos|-----------| - I*\/ 2 *sin|-----------||*|- \/ 2 *cos|-----------| + I*\/ 2 *sin|-----------||*|\/ 2 *cos|-----------| - I*\/ 2 *sin|-----------||*|\/ 2 *cos|-----------| + I*\/ 2 *sin|-----------||
\ \ 2 / \ 2 // \ \ 2 / \ 2 // \ \ 2 / \ 2 // \ \ 2 / \ 2 //
( − 2 cos ( atan ( 7 3 ) 2 ) − 2 i sin ( atan ( 7 3 ) 2 ) ) ( − 2 cos ( atan ( 7 3 ) 2 ) + 2 i sin ( atan ( 7 3 ) 2 ) ) ( 2 cos ( atan ( 7 3 ) 2 ) − 2 i sin ( atan ( 7 3 ) 2 ) ) ( 2 cos ( atan ( 7 3 ) 2 ) + 2 i sin ( atan ( 7 3 ) 2 ) ) \left(- \sqrt{2} \cos{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)} - \sqrt{2} i \sin{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)}\right) \left(- \sqrt{2} \cos{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)} + \sqrt{2} i \sin{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)}\right) \left(\sqrt{2} \cos{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)} - \sqrt{2} i \sin{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)}\right) \left(\sqrt{2} \cos{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)} + \sqrt{2} i \sin{\left(\frac{\operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}}{2} \right)}\right) − 2 cos 2 atan ( 3 7 ) − 2 i sin 2 atan ( 3 7 ) − 2 cos 2 atan ( 3 7 ) + 2 i sin 2 atan ( 3 7 ) 2 cos 2 atan ( 3 7 ) − 2 i sin 2 atan ( 3 7 ) 2 cos 2 atan ( 3 7 ) + 2 i sin 2 atan ( 3 7 )
/ ___\
|\/ 7 |
/ ___\ I*atan|-----|
|3 I*\/ 7 | \ 3 /
4*|- - -------|*e
\4 4 /
4 ( 3 4 − 7 i 4 ) e i atan ( 7 3 ) 4 \left(\frac{3}{4} - \frac{\sqrt{7} i}{4}\right) e^{i \operatorname{atan}{\left(\frac{\sqrt{7}}{3} \right)}} 4 ( 4 3 − 4 7 i ) e i atan ( 3 7 )
4*(3/4 - i*sqrt(7)/4)*exp(i*atan(sqrt(7)/3))
x1 = 1.3228756555323 + 0.5*i
x2 = -1.3228756555323 + 0.5*i
x3 = -1.3228756555323 - 0.5*i
x4 = 1.3228756555323 - 0.5*i
x4 = 1.3228756555323 - 0.5*i