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2sin^2(x)-5cos(x)+1=0 la ecuación

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Solución numérica:

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Solución

Ha introducido [src]
     2                      
2*sin (x) - 5*cos(x) + 1 = 0
$$\left(2 \sin^{2}{\left(x \right)} - 5 \cos{\left(x \right)}\right) + 1 = 0$$
Solución detallada
Tenemos la ecuación
$$\left(2 \sin^{2}{\left(x \right)} - 5 \cos{\left(x \right)}\right) + 1 = 0$$
cambiamos
$$- 5 \cos{\left(x \right)} - \cos{\left(2 x \right)} + 2 = 0$$
$$- 2 \cos^{2}{\left(x \right)} - 5 \cos{\left(x \right)} + 3 = 0$$
Sustituimos
$$w = \cos{\left(x \right)}$$
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:
$$w_{1} = \frac{\sqrt{D} - b}{2 a}$$
$$w_{2} = \frac{- \sqrt{D} - b}{2 a}$$
donde D = b^2 - 4*a*c es el discriminante.
Como
$$a = -2$$
$$b = -5$$
$$c = 3$$
, entonces
D = b^2 - 4 * a * c = 

(-5)^2 - 4 * (-2) * (3) = 49

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

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

o
$$w_{1} = -3$$
$$w_{2} = \frac{1}{2}$$
hacemos cambio inverso
$$\cos{\left(x \right)} = w$$
Tenemos la ecuación
$$\cos{\left(x \right)} = w$$
es la ecuación trigonométrica más simple
Esta ecuación se reorganiza en
$$x = \pi n + \operatorname{acos}{\left(w \right)}$$
$$x = \pi n + \operatorname{acos}{\left(w \right)} - \pi$$
O
$$x = \pi n + \operatorname{acos}{\left(w \right)}$$
$$x = \pi n + \operatorname{acos}{\left(w \right)} - \pi$$
, donde n es cualquier número entero
sustituimos w:
$$x_{1} = \pi n + \operatorname{acos}{\left(w_{1} \right)}$$
$$x_{1} = \pi n + \operatorname{acos}{\left(-3 \right)}$$
$$x_{1} = \pi n + \operatorname{acos}{\left(-3 \right)}$$
$$x_{2} = \pi n + \operatorname{acos}{\left(w_{2} \right)}$$
$$x_{2} = \pi n + \operatorname{acos}{\left(\frac{1}{2} \right)}$$
$$x_{2} = \pi n + \frac{\pi}{3}$$
$$x_{3} = \pi n + \operatorname{acos}{\left(w_{1} \right)} - \pi$$
$$x_{3} = \pi n - \pi + \operatorname{acos}{\left(-3 \right)}$$
$$x_{3} = \pi n - \pi + \operatorname{acos}{\left(-3 \right)}$$
$$x_{4} = \pi n + \operatorname{acos}{\left(w_{2} \right)} - \pi$$
$$x_{4} = \pi n - \pi + \operatorname{acos}{\left(\frac{1}{2} \right)}$$
$$x_{4} = \pi n - \frac{2 \pi}{3}$$
Gráfica
Suma y producto de raíces [src]
suma
  pi   pi       /     /  ___\\         /     /  ___\\         /     /  ___\\         /     /  ___\\
- -- + -- + 2*im\atanh\\/ 2 // - 2*I*re\atanh\\/ 2 // + - 2*im\atanh\\/ 2 // + 2*I*re\atanh\\/ 2 //
  3    3                                                                                           
$$\left(\left(- \frac{\pi}{3} + \frac{\pi}{3}\right) + \left(2 \operatorname{im}{\left(\operatorname{atanh}{\left(\sqrt{2} \right)}\right)} - 2 i \operatorname{re}{\left(\operatorname{atanh}{\left(\sqrt{2} \right)}\right)}\right)\right) + \left(- 2 \operatorname{im}{\left(\operatorname{atanh}{\left(\sqrt{2} \right)}\right)} + 2 i \operatorname{re}{\left(\operatorname{atanh}{\left(\sqrt{2} \right)}\right)}\right)$$
=
0
$$0$$
producto
-pi  pi /    /     /  ___\\         /     /  ___\\\ /      /     /  ___\\         /     /  ___\\\
----*--*\2*im\atanh\\/ 2 // - 2*I*re\atanh\\/ 2 ///*\- 2*im\atanh\\/ 2 // + 2*I*re\atanh\\/ 2 ///
 3   3                                                                                           
$$- \frac{\pi}{3} \frac{\pi}{3} \left(2 \operatorname{im}{\left(\operatorname{atanh}{\left(\sqrt{2} \right)}\right)} - 2 i \operatorname{re}{\left(\operatorname{atanh}{\left(\sqrt{2} \right)}\right)}\right) \left(- 2 \operatorname{im}{\left(\operatorname{atanh}{\left(\sqrt{2} \right)}\right)} + 2 i \operatorname{re}{\left(\operatorname{atanh}{\left(\sqrt{2} \right)}\right)}\right)$$
=
                                               2
    2 /      /     /  ___\\     /     /  ___\\\ 
4*pi *\- I*re\atanh\\/ 2 // + im\atanh\\/ 2 /// 
------------------------------------------------
                       9                        
$$\frac{4 \pi^{2} \left(\operatorname{im}{\left(\operatorname{atanh}{\left(\sqrt{2} \right)}\right)} - i \operatorname{re}{\left(\operatorname{atanh}{\left(\sqrt{2} \right)}\right)}\right)^{2}}{9}$$
4*pi^2*(-i*re(atanh(sqrt(2))) + im(atanh(sqrt(2))))^2/9
Respuesta rápida [src]
     -pi 
x1 = ----
      3  
$$x_{1} = - \frac{\pi}{3}$$
     pi
x2 = --
     3 
$$x_{2} = \frac{\pi}{3}$$
         /     /  ___\\         /     /  ___\\
x3 = 2*im\atanh\\/ 2 // - 2*I*re\atanh\\/ 2 //
$$x_{3} = 2 \operatorname{im}{\left(\operatorname{atanh}{\left(\sqrt{2} \right)}\right)} - 2 i \operatorname{re}{\left(\operatorname{atanh}{\left(\sqrt{2} \right)}\right)}$$
           /     /  ___\\         /     /  ___\\
x4 = - 2*im\atanh\\/ 2 // + 2*I*re\atanh\\/ 2 //
$$x_{4} = - 2 \operatorname{im}{\left(\operatorname{atanh}{\left(\sqrt{2} \right)}\right)} + 2 i \operatorname{re}{\left(\operatorname{atanh}{\left(\sqrt{2} \right)}\right)}$$
x4 = -2*im(atanh(sqrt(2))) + 2*i*re(atanh(sqrt(2)))
Respuesta numérica [src]
x1 = -55.5014702134197
x2 = 11.5191730631626
x3 = 99.4837673636768
x4 = -11.5191730631626
x5 = -42.9350995990605
x6 = -30.3687289847013
x7 = -1.0471975511966
x8 = -89.0117918517108
x9 = -38.7463093942741
x10 = 30.3687289847013
x11 = -49.2182849062401
x12 = -32.4631240870945
x13 = 36.6519142918809
x14 = 38.7463093942741
x15 = 93.2005820564972
x16 = -74.3510261349584
x17 = 74.3510261349584
x18 = 55.5014702134197
x19 = 1.0471975511966
x20 = 51.3126800086333
x21 = 17.8023583703422
x22 = -51.3126800086333
x23 = 95.2949771588904
x24 = -57.5958653158129
x25 = -99.4837673636768
x26 = -82.7286065445312
x27 = 26.1799387799149
x28 = 76.4454212373516
x29 = 57.5958653158129
x30 = 82.7286065445312
x31 = 86.9173967493176
x32 = 24.0855436775217
x33 = -61.7846555205993
x34 = -4503.99666769657
x35 = -17.8023583703422
x36 = -26.1799387799149
x37 = 5.23598775598299
x38 = 49.2182849062401
x39 = 45.0294947014537
x40 = 32.4631240870945
x41 = 70.162235930172
x42 = -70.162235930172
x43 = -105.766952670856
x44 = -80.634211442138
x45 = 109898.147010327
x46 = -5.23598775598299
x47 = 89.0117918517108
x48 = -68.0678408277789
x49 = 80.634211442138
x50 = -24.0855436775217
x51 = -95.2949771588904
x52 = -13.6135681655558
x53 = 61.7846555205993
x54 = -93.2005820564972
x55 = 63.8790506229925
x56 = -76.4454212373516
x57 = -63.8790506229925
x58 = 42.9350995990605
x59 = -36.6519142918809
x60 = 68.0678408277789
x61 = -7.33038285837618
x62 = -19.8967534727354
x63 = -45.0294947014537
x64 = 19.8967534727354
x65 = 7.33038285837618
x66 = -86.9173967493176
x67 = 13.6135681655558
x67 = 13.6135681655558