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cos(2x)=-(2/5) la ecuación

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Solución numérica:

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Solución

Ha introducido [src]
cos(2*x) = -2/5
$$\cos{\left(2 x \right)} = - \frac{2}{5}$$
Solución detallada
Tenemos la ecuación
$$\cos{\left(2 x \right)} = - \frac{2}{5}$$
es la ecuación trigonométrica más simple
Esta ecuación se reorganiza en
$$2 x = \pi n + \operatorname{acos}{\left(- \frac{2}{5} \right)}$$
$$2 x = \pi n - \pi + \operatorname{acos}{\left(- \frac{2}{5} \right)}$$
O
$$2 x = \pi n + \operatorname{acos}{\left(- \frac{2}{5} \right)}$$
$$2 x = \pi n - \pi + \operatorname{acos}{\left(- \frac{2}{5} \right)}$$
, donde n es cualquier número entero
Dividamos ambos miembros de la ecuación obtenida en
$$2$$
obtenemos la respuesta:
$$x_{1} = \frac{\pi n}{2} + \frac{\operatorname{acos}{\left(- \frac{2}{5} \right)}}{2}$$
$$x_{2} = \frac{\pi n}{2} - \frac{\pi}{2} + \frac{\operatorname{acos}{\left(- \frac{2}{5} \right)}}{2}$$
Gráfica
Suma y producto de raíces [src]
suma
     acos(-2/5)   acos(-2/5)
pi - ---------- + ----------
         2            2     
$$\frac{\operatorname{acos}{\left(- \frac{2}{5} \right)}}{2} + \left(\pi - \frac{\operatorname{acos}{\left(- \frac{2}{5} \right)}}{2}\right)$$
=
pi
$$\pi$$
producto
/     acos(-2/5)\ acos(-2/5)
|pi - ----------|*----------
\         2     /     2     
$$\left(\pi - \frac{\operatorname{acos}{\left(- \frac{2}{5} \right)}}{2}\right) \frac{\operatorname{acos}{\left(- \frac{2}{5} \right)}}{2}$$
=
(-acos(-2/5) + 2*pi)*acos(-2/5)
-------------------------------
               4               
$$\frac{\left(- \operatorname{acos}{\left(- \frac{2}{5} \right)} + 2 \pi\right) \operatorname{acos}{\left(- \frac{2}{5} \right)}}{4}$$
(-acos(-2/5) + 2*pi)*acos(-2/5)/4
Respuesta rápida [src]
          acos(-2/5)
x1 = pi - ----------
              2     
$$x_{1} = \pi - \frac{\operatorname{acos}{\left(- \frac{2}{5} \right)}}{2}$$
     acos(-2/5)
x2 = ----------
         2     
$$x_{2} = \frac{\operatorname{acos}{\left(- \frac{2}{5} \right)}}{2}$$
x2 = acos(-2/5)/2
Respuesta numérica [src]
x1 = 24.1415846422872
x2 = -71.265474446134
x3 = 83.8318450604932
x4 = 8.43362137433819
x5 = 22.9823051615597
x6 = 48.1150463902781
x7 = -82.6725655797658
x8 = 82.6725655797658
x9 = 32.4070831223291
x10 = -76.3893802725862
x11 = 16.6991198543802
x12 = 90.1150303676728
x13 = 70.1061949654066
x14 = -41.8318610830985
x15 = -98.3805288477148
x16 = -70.1061949654066
x17 = 2.1504360671586
x18 = -90.1150303676728
x19 = -57.5398243510475
x20 = -13.5575272007904
x21 = 92.0973435405352
x22 = 770.681356715931
x23 = -46.1327332174157
x24 = 52.4159185245953
x25 = -10.4159345472006
x26 = 46.1327332174157
x27 = -32.4070831223291
x28 = -33.5663626030565
x29 = -2.1504360671586
x30 = 68.1238817925443
x31 = 85.8141582333556
x32 = 33.5663626030565
x33 = -17.8583993351076
x34 = -4.13274924002099
x35 = 99.5398083284422
x36 = -79.530972926176
x37 = 74.4070670997238
x38 = 874.353914284394
x39 = 41.8318610830985
x40 = 58.6991038317749
x41 = 61.8406964853647
x42 = 98.3805288477148
x43 = -27.2831772958769
x44 = -93.2566230212626
x45 = -63.8230096582271
x46 = 76.3893802725862
x47 = 64.9822891389545
x48 = -39.8495479102361
x49 = 55.5575111781851
x50 = -35.5486757759189
x51 = -54.3982316974577
x52 = -19.84071250797
x53 = 4.13274924002099
x54 = -85.8141582333556
x55 = -77.5486597533136
x56 = 17.8583993351076
x57 = -68.1238817925443
x58 = 10.4159345472006
x59 = -83.8318450604932
x60 = 54.3982316974577
x61 = -5.29202872074839
x62 = -99.5398083284422
x63 = -55.5575111781851
x64 = -14.7168066815178
x65 = 39.8495479102361
x66 = 63.8230096582271
x67 = 19.84071250797
x68 = -24.1415846422872
x69 = 60.6814170046373
x70 = 30.4247699494667
x71 = -49.2743258710055
x72 = 77.5486597533136
x73 = 96.3982156748524
x74 = 11.575214027928
x75 = -48.1150463902781
x76 = -29.2654904687393
x77 = -61.8406964853647
x78 = 26.1238978151495
x79 = -92.0973435405352
x80 = 38.6902684295087
x81 = -11.575214027928
x82 = -26.1238978151495
x83 = -101424.168385079
x83 = -101424.168385079