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sin^2x-sinx-1>0

sin^2x-sinx-1>0 desigualdades

En la desigualdad la incógnita

Solución

Ha introducido [src]
   2                    
sin (x) - sin(x) - 1 > 0
(sin2(x)sin(x))1>0\left(\sin^{2}{\left(x \right)} - \sin{\left(x \right)}\right) - 1 > 0
sin(x)^2 - sin(x) - 1 > 0
Solución detallada
Se da la desigualdad:
(sin2(x)sin(x))1>0\left(\sin^{2}{\left(x \right)} - \sin{\left(x \right)}\right) - 1 > 0
Para resolver esta desigualdad primero hay que resolver la ecuación correspondiente:
(sin2(x)sin(x))1=0\left(\sin^{2}{\left(x \right)} - \sin{\left(x \right)}\right) - 1 = 0
Resolvemos:
Tenemos la ecuación
(sin2(x)sin(x))1=0\left(\sin^{2}{\left(x \right)} - \sin{\left(x \right)}\right) - 1 = 0
cambiamos
sin2(x)sin(x)1=0\sin^{2}{\left(x \right)} - \sin{\left(x \right)} - 1 = 0
(sin2(x)sin(x))1=0\left(\sin^{2}{\left(x \right)} - \sin{\left(x \right)}\right) - 1 = 0
Sustituimos
w=sin(x)w = \sin{\left(x \right)}
Es la ecuación de la forma
a*w^2 + b*w + c = 0

La ecuación cuadrática puede ser resuelta
con la ayuda del discriminante.
Las raíces de la ecuación cuadrática:
w1=Db2aw_{1} = \frac{\sqrt{D} - b}{2 a}
w2=Db2aw_{2} = \frac{- \sqrt{D} - b}{2 a}
donde D = b^2 - 4*a*c es el discriminante.
Como
a=1a = 1
b=1b = -1
c=1c = -1
, entonces
D = b^2 - 4 * a * c = 

(-1)^2 - 4 * (1) * (-1) = 5

Como D > 0 la ecuación tiene dos raíces.
w1 = (-b + sqrt(D)) / (2*a)

w2 = (-b - sqrt(D)) / (2*a)

o
w1=12+52w_{1} = \frac{1}{2} + \frac{\sqrt{5}}{2}
w2=1252w_{2} = \frac{1}{2} - \frac{\sqrt{5}}{2}
hacemos cambio inverso
sin(x)=w\sin{\left(x \right)} = w
Tenemos la ecuación
sin(x)=w\sin{\left(x \right)} = w
es la ecuación trigonométrica más simple
Esta ecuación se reorganiza en
x=2πn+asin(w)x = 2 \pi n + \operatorname{asin}{\left(w \right)}
x=2πnasin(w)+πx = 2 \pi n - \operatorname{asin}{\left(w \right)} + \pi
O
x=2πn+asin(w)x = 2 \pi n + \operatorname{asin}{\left(w \right)}
x=2πnasin(w)+πx = 2 \pi n - \operatorname{asin}{\left(w \right)} + \pi
, donde n es cualquier número entero
sustituimos w:
x1=2πn+asin(w1)x_{1} = 2 \pi n + \operatorname{asin}{\left(w_{1} \right)}
x1=2πn+asin(12+52)x_{1} = 2 \pi n + \operatorname{asin}{\left(\frac{1}{2} + \frac{\sqrt{5}}{2} \right)}
x1=2πn+asin(12+52)x_{1} = 2 \pi n + \operatorname{asin}{\left(\frac{1}{2} + \frac{\sqrt{5}}{2} \right)}
x2=2πn+asin(w2)x_{2} = 2 \pi n + \operatorname{asin}{\left(w_{2} \right)}
x2=2πn+asin(1252)x_{2} = 2 \pi n + \operatorname{asin}{\left(\frac{1}{2} - \frac{\sqrt{5}}{2} \right)}
x2=2πn+asin(1252)x_{2} = 2 \pi n + \operatorname{asin}{\left(\frac{1}{2} - \frac{\sqrt{5}}{2} \right)}
x3=2πnasin(w1)+πx_{3} = 2 \pi n - \operatorname{asin}{\left(w_{1} \right)} + \pi
x3=2πn+πasin(12+52)x_{3} = 2 \pi n + \pi - \operatorname{asin}{\left(\frac{1}{2} + \frac{\sqrt{5}}{2} \right)}
x3=2πn+πasin(12+52)x_{3} = 2 \pi n + \pi - \operatorname{asin}{\left(\frac{1}{2} + \frac{\sqrt{5}}{2} \right)}
x4=2πnasin(w2)+πx_{4} = 2 \pi n - \operatorname{asin}{\left(w_{2} \right)} + \pi
x4=2πnasin(1252)+πx_{4} = 2 \pi n - \operatorname{asin}{\left(\frac{1}{2} - \frac{\sqrt{5}}{2} \right)} + \pi
x4=2πnasin(1252)+πx_{4} = 2 \pi n - \operatorname{asin}{\left(\frac{1}{2} - \frac{\sqrt{5}}{2} \right)} + \pi
x1=πasin(1252)x_{1} = \pi - \operatorname{asin}{\left(\frac{1}{2} - \frac{\sqrt{5}}{2} \right)}
x2=πasin(12+52)x_{2} = \pi - \operatorname{asin}{\left(\frac{1}{2} + \frac{\sqrt{5}}{2} \right)}
x3=asin(1252)x_{3} = \operatorname{asin}{\left(\frac{1}{2} - \frac{\sqrt{5}}{2} \right)}
x4=asin(12+52)x_{4} = \operatorname{asin}{\left(\frac{1}{2} + \frac{\sqrt{5}}{2} \right)}
Descartamos las soluciones complejas:
x1=πasin(1252)x_{1} = \pi - \operatorname{asin}{\left(\frac{1}{2} - \frac{\sqrt{5}}{2} \right)}
x2=asin(1252)x_{2} = \operatorname{asin}{\left(\frac{1}{2} - \frac{\sqrt{5}}{2} \right)}
Las raíces dadas
x2=asin(1252)x_{2} = \operatorname{asin}{\left(\frac{1}{2} - \frac{\sqrt{5}}{2} \right)}
x1=πasin(1252)x_{1} = \pi - \operatorname{asin}{\left(\frac{1}{2} - \frac{\sqrt{5}}{2} \right)}
son puntos de cambio del signo de desigualdad en las soluciones.
Primero definámonos con el signo hasta el punto extremo izquierdo:
x0<x2x_{0} < x_{2}
Consideremos, por ejemplo, el punto
x0=x2110x_{0} = x_{2} - \frac{1}{10}
=
asin(1252)+110\operatorname{asin}{\left(\frac{1}{2} - \frac{\sqrt{5}}{2} \right)} + - \frac{1}{10}
=
asin(1252)110\operatorname{asin}{\left(\frac{1}{2} - \frac{\sqrt{5}}{2} \right)} - \frac{1}{10}
lo sustituimos en la expresión
(sin2(x)sin(x))1>0\left(\sin^{2}{\left(x \right)} - \sin{\left(x \right)}\right) - 1 > 0
(sin2(asin(1252)110)sin(asin(1252)110))1>0\left(\sin^{2}{\left(\operatorname{asin}{\left(\frac{1}{2} - \frac{\sqrt{5}}{2} \right)} - \frac{1}{10} \right)} - \sin{\left(\operatorname{asin}{\left(\frac{1}{2} - \frac{\sqrt{5}}{2} \right)} - \frac{1}{10} \right)}\right) - 1 > 0
         /           /      ___\\      /           /      ___\\    
        2|  1        |1   \/ 5 ||      |  1        |1   \/ 5 ||    
-1 + sin |- -- + asin|- - -----|| - sin|- -- + asin|- - -----|| > 0
         \  10       \2     2  //      \  10       \2     2  //    
    

significa que una de las soluciones de nuestra ecuación será con:
x<asin(1252)x < \operatorname{asin}{\left(\frac{1}{2} - \frac{\sqrt{5}}{2} \right)}
 _____           _____          
      \         /
-------ο-------ο-------
       x2      x1

Recibiremos otras soluciones de la desigualdad pasando al polo siguiente etc.
etc.
Respuesta:
x<asin(1252)x < \operatorname{asin}{\left(\frac{1}{2} - \frac{\sqrt{5}}{2} \right)}
x>πasin(1252)x > \pi - \operatorname{asin}{\left(\frac{1}{2} - \frac{\sqrt{5}}{2} \right)}
Solución de la desigualdad en el gráfico
0-60-50-40-30-20-101020304050602.5-2.5
Respuesta rápida [src]
   /               /  ___ /      ___\\           /  ___ /      ___\\    \
   |               |\/ 2 *\1 - \/ 5 /|           |\/ 2 *\1 - \/ 5 /|    |
And|x < 2*pi + atan|-----------------|, pi - atan|-----------------| < x|
   |               |     ____________|           |     ____________|    |
   |               |    /        ___ |           |    /        ___ |    |
   \               \2*\/  -1 + \/ 5  /           \2*\/  -1 + \/ 5  /    /
x<atan(2(15)21+5)+2ππatan(2(15)21+5)<xx < \operatorname{atan}{\left(\frac{\sqrt{2} \left(1 - \sqrt{5}\right)}{2 \sqrt{-1 + \sqrt{5}}} \right)} + 2 \pi \wedge \pi - \operatorname{atan}{\left(\frac{\sqrt{2} \left(1 - \sqrt{5}\right)}{2 \sqrt{-1 + \sqrt{5}}} \right)} < x
(x < 2*pi + atan(sqrt(2)*(1 - sqrt(5))/(2*sqrt(-1 + sqrt(5)))))∧(pi - atan(sqrt(2)*(1 - sqrt(5))/(2*sqrt(-1 + sqrt(5)))) < x)
Respuesta rápida 2 [src]
          /  ___ /      ___\\             /  ___ /      ___\\ 
          |\/ 2 *\1 - \/ 5 /|             |\/ 2 *\1 - \/ 5 /| 
(pi - atan|-----------------|, 2*pi + atan|-----------------|)
          |     ____________|             |     ____________| 
          |    /        ___ |             |    /        ___ | 
          \2*\/  -1 + \/ 5  /             \2*\/  -1 + \/ 5  / 
x in (πatan(2(15)21+5),atan(2(15)21+5)+2π)x\ in\ \left(\pi - \operatorname{atan}{\left(\frac{\sqrt{2} \left(1 - \sqrt{5}\right)}{2 \sqrt{-1 + \sqrt{5}}} \right)}, \operatorname{atan}{\left(\frac{\sqrt{2} \left(1 - \sqrt{5}\right)}{2 \sqrt{-1 + \sqrt{5}}} \right)} + 2 \pi\right)
x in Interval.open(pi - atan(sqrt(2)*(1 - sqrt(5))/(2*sqrt(-1 + sqrt(5)))), atan(sqrt(2)*(1 - sqrt(5))/(2*sqrt(-1 + sqrt(5)))) + 2*pi)
Gráfico
sin^2x-sinx-1>0 desigualdades