Resuelve las siguientes ecuaciones para 0 < x < 2 pi
6. a) 2cos x + 3 = 2
7. b) sen3x - 2 = -3sen3x
8. c) senx(2 - senx) = cos2x
gianluigi081:
Sen 3x o elevado a la 3?
Respuestas
Respuesta dada por:
27
Resuelve las siguientes ecuaciones para 0 < x < 2π
6. a) 2cos x + 3 = 2
7. b) sen3x - 2 = -3sen3x
8. c) senx(2 - senx) = cos2x
Resolvemos:
![a) \\ 2\cos \left(x\right)+3=2 \Rightarrow 0\ \textless \ x\ \textless \ 2\pi \\ \\ 2\cos \left(x\right)=2-3 \\ \\ 2\cos \left(x\right)=-1 \\ \\ Despejamos \\ \\ \cos \left(x\right)=-\frac{1}{2} \\ \\ \cos \left(x\right)=-\frac{1}{2}:\quad x=\frac{2\pi }{3}+2\pi n,\:\quad x=\frac{4\pi }{3}+2\pi n \\ \\ \boxed{x=\frac{2\pi }{3},\:x=\frac{4\pi }{3}} \ \surd a) \\ 2\cos \left(x\right)+3=2 \Rightarrow 0\ \textless \ x\ \textless \ 2\pi \\ \\ 2\cos \left(x\right)=2-3 \\ \\ 2\cos \left(x\right)=-1 \\ \\ Despejamos \\ \\ \cos \left(x\right)=-\frac{1}{2} \\ \\ \cos \left(x\right)=-\frac{1}{2}:\quad x=\frac{2\pi }{3}+2\pi n,\:\quad x=\frac{4\pi }{3}+2\pi n \\ \\ \boxed{x=\frac{2\pi }{3},\:x=\frac{4\pi }{3}} \ \surd](https://tex.z-dn.net/?f=a%29+%5C%5C+2%5Ccos+%5Cleft%28x%5Cright%29%2B3%3D2+%5CRightarrow+0%5C+%5Ctextless+%5C+x%5C+%5Ctextless+%5C+2%5Cpi+%5C%5C+%5C%5C++2%5Ccos+%5Cleft%28x%5Cright%29%3D2-3+%5C%5C+%5C%5C+2%5Ccos+%5Cleft%28x%5Cright%29%3D-1+%5C%5C+%5C%5C+Despejamos+%5C%5C+%5C%5C+%5Ccos+%5Cleft%28x%5Cright%29%3D-%5Cfrac%7B1%7D%7B2%7D+%5C%5C+%5C%5C+%5Ccos+%5Cleft%28x%5Cright%29%3D-%5Cfrac%7B1%7D%7B2%7D%3A%5Cquad+x%3D%5Cfrac%7B2%5Cpi+%7D%7B3%7D%2B2%5Cpi+n%2C%5C%3A%5Cquad+x%3D%5Cfrac%7B4%5Cpi+%7D%7B3%7D%2B2%5Cpi+n+%5C%5C++%5C%5C+%5Cboxed%7Bx%3D%5Cfrac%7B2%5Cpi+%7D%7B3%7D%2C%5C%3Ax%3D%5Cfrac%7B4%5Cpi+%7D%7B3%7D%7D+%5C+%5Csurd+)
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![b) \\ \\ sen \left(3x\right)-2=-3 sen \left(3x\right)\Rightarrow\:0\ \textless \ x\ \textless \ 2\pi \\ \\ Hacemos \ una \ sustituci\'on: \\ \\ u=sen(3x) \\ \\ Reescribimos: \\ \\ u-2=-3u \\ \\ Agrupamos \ t\'erminos \ semejantes: \\ \\ u+3u=2 \\ \\ Hacemos \ las \ operaciones: \\ \\ 4u=2 \\ \\ u= \frac{4}{2} \\ \\ u=2 \\ \\ Regresamos \ a \ la \ original: \\ \\ sen \left(3x\right)=\frac{1}{2} \\ \\ sen \left(3x\right)=\frac{1}{2}:\quad 3x=\frac{\pi }{6}+2\pi n,\:\quad 3x=\frac{5\pi }{6}+2\pi n \\ \\ b) \\ \\ sen \left(3x\right)-2=-3 sen \left(3x\right)\Rightarrow\:0\ \textless \ x\ \textless \ 2\pi \\ \\ Hacemos \ una \ sustituci\'on: \\ \\ u=sen(3x) \\ \\ Reescribimos: \\ \\ u-2=-3u \\ \\ Agrupamos \ t\'erminos \ semejantes: \\ \\ u+3u=2 \\ \\ Hacemos \ las \ operaciones: \\ \\ 4u=2 \\ \\ u= \frac{4}{2} \\ \\ u=2 \\ \\ Regresamos \ a \ la \ original: \\ \\ sen \left(3x\right)=\frac{1}{2} \\ \\ sen \left(3x\right)=\frac{1}{2}:\quad 3x=\frac{\pi }{6}+2\pi n,\:\quad 3x=\frac{5\pi }{6}+2\pi n \\ \\](https://tex.z-dn.net/?f=b%29++%5C%5C++%5C%5C+sen+%5Cleft%283x%5Cright%29-2%3D-3+sen+%5Cleft%283x%5Cright%29%5CRightarrow%5C%3A0%5C+%5Ctextless+%5C+x%5C+%5Ctextless+%5C+2%5Cpi++%5C%5C++%5C%5C+Hacemos+%5C+una+%5C+sustituci%5C%27on%3A++%5C%5C++%5C%5C+u%3Dsen%283x%29+%5C%5C++%5C%5C+Reescribimos%3A+%5C%5C++%5C%5C+u-2%3D-3u+%5C%5C++%5C%5C+Agrupamos+%5C+t%5C%27erminos+%5C+semejantes%3A+%5C%5C++%5C%5C+u%2B3u%3D2+%5C%5C++%5C%5C+Hacemos+%5C+las+%5C+operaciones%3A+%5C%5C++%5C%5C+4u%3D2+%5C%5C++%5C%5C+u%3D+%5Cfrac%7B4%7D%7B2%7D+%5C%5C++%5C%5C+u%3D2+%5C%5C++%5C%5C+Regresamos+%5C+a+%5C+la+%5C+original%3A+%5C%5C++%5C%5C++sen+%5Cleft%283x%5Cright%29%3D%5Cfrac%7B1%7D%7B2%7D+%5C%5C++%5C%5C+sen+%5Cleft%283x%5Cright%29%3D%5Cfrac%7B1%7D%7B2%7D%3A%5Cquad+3x%3D%5Cfrac%7B%5Cpi+%7D%7B6%7D%2B2%5Cpi+n%2C%5C%3A%5Cquad+3x%3D%5Cfrac%7B5%5Cpi+%7D%7B6%7D%2B2%5Cpi+n+%5C%5C++%5C%5C+)
![Resolvemos: \\ \\ 3x=\frac{\pi }{6}+2\pi n \\ \\ x=\frac{\frac{\pi }{6}}{3}+\frac{2\pi n}{3} \\ \\ x=\frac{\frac{\pi }{6}+2\pi n}{3} \\ \\ x=\frac{\pi +12\pi n}{3\cdot \:6} \\ \\ x=\frac{\pi +12\pi n}{18} \\ \\ Ahora \ resolvemos \ este \\ \\ 3x=\frac{5\pi }{6}+2\pi n \\ \\ x=\frac{\frac{5\pi }{6}}{3}+\frac{2\pi n}{3} \\ \\ Mcm= 6 \\ \\ x=\frac{5\pi +2\cdot \:6\pi n}{6} \\ \\ x=\frac{\frac{5\pi +12\pi n}{6}}{3} \\ \\ x=\frac{5\pi +12\pi n}{18} \\ \\ Unimos \\ \\ Resolvemos: \\ \\ 3x=\frac{\pi }{6}+2\pi n \\ \\ x=\frac{\frac{\pi }{6}}{3}+\frac{2\pi n}{3} \\ \\ x=\frac{\frac{\pi }{6}+2\pi n}{3} \\ \\ x=\frac{\pi +12\pi n}{3\cdot \:6} \\ \\ x=\frac{\pi +12\pi n}{18} \\ \\ Ahora \ resolvemos \ este \\ \\ 3x=\frac{5\pi }{6}+2\pi n \\ \\ x=\frac{\frac{5\pi }{6}}{3}+\frac{2\pi n}{3} \\ \\ Mcm= 6 \\ \\ x=\frac{5\pi +2\cdot \:6\pi n}{6} \\ \\ x=\frac{\frac{5\pi +12\pi n}{6}}{3} \\ \\ x=\frac{5\pi +12\pi n}{18} \\ \\ Unimos \\ \\](https://tex.z-dn.net/?f=Resolvemos%3A+%5C%5C+%5C%5C+3x%3D%5Cfrac%7B%5Cpi+%7D%7B6%7D%2B2%5Cpi+n+%5C%5C+%5C%5C+x%3D%5Cfrac%7B%5Cfrac%7B%5Cpi+%7D%7B6%7D%7D%7B3%7D%2B%5Cfrac%7B2%5Cpi+n%7D%7B3%7D+%5C%5C+%5C%5C+x%3D%5Cfrac%7B%5Cfrac%7B%5Cpi+%7D%7B6%7D%2B2%5Cpi+n%7D%7B3%7D+%5C%5C+%5C%5C+x%3D%5Cfrac%7B%5Cpi+%2B12%5Cpi+n%7D%7B3%5Ccdot+%5C%3A6%7D+%5C%5C+%5C%5C+x%3D%5Cfrac%7B%5Cpi+%2B12%5Cpi+n%7D%7B18%7D+%5C%5C+%5C%5C+Ahora+%5C+resolvemos+%5C+este+%5C%5C+%5C%5C+3x%3D%5Cfrac%7B5%5Cpi+%7D%7B6%7D%2B2%5Cpi+n+%5C%5C+%5C%5C+x%3D%5Cfrac%7B%5Cfrac%7B5%5Cpi+%7D%7B6%7D%7D%7B3%7D%2B%5Cfrac%7B2%5Cpi+n%7D%7B3%7D+%5C%5C+%5C%5C+Mcm%3D+6+%5C%5C+%5C%5C+x%3D%5Cfrac%7B5%5Cpi+%2B2%5Ccdot+%5C%3A6%5Cpi+n%7D%7B6%7D+%5C%5C+%5C%5C+x%3D%5Cfrac%7B%5Cfrac%7B5%5Cpi+%2B12%5Cpi+n%7D%7B6%7D%7D%7B3%7D+%5C%5C+%5C%5C+x%3D%5Cfrac%7B5%5Cpi+%2B12%5Cpi+n%7D%7B18%7D+%5C%5C+%5C%5C+Unimos+%5C%5C+%5C%5C+)
![x=\frac{\pi +12\pi n}{18},\:x=\frac{5\pi +12\pi n}{18} \\ \\ Entonces \\ \\ \boxed{x=\frac{\pi }{18},\:x=\frac{5\pi }{18},\:x=\frac{13\pi }{18},\:x=\frac{17\pi }{18},\:x=\frac{25\pi }{18},\:x=\frac{29\pi }{18}} \ \surd x=\frac{\pi +12\pi n}{18},\:x=\frac{5\pi +12\pi n}{18} \\ \\ Entonces \\ \\ \boxed{x=\frac{\pi }{18},\:x=\frac{5\pi }{18},\:x=\frac{13\pi }{18},\:x=\frac{17\pi }{18},\:x=\frac{25\pi }{18},\:x=\frac{29\pi }{18}} \ \surd](https://tex.z-dn.net/?f=x%3D%5Cfrac%7B%5Cpi+%2B12%5Cpi+n%7D%7B18%7D%2C%5C%3Ax%3D%5Cfrac%7B5%5Cpi+%2B12%5Cpi+n%7D%7B18%7D++%5C%5C++%5C%5C+Entonces++%5C%5C++%5C%5C+%5Cboxed%7Bx%3D%5Cfrac%7B%5Cpi+%7D%7B18%7D%2C%5C%3Ax%3D%5Cfrac%7B5%5Cpi+%7D%7B18%7D%2C%5C%3Ax%3D%5Cfrac%7B13%5Cpi+%7D%7B18%7D%2C%5C%3Ax%3D%5Cfrac%7B17%5Cpi+%7D%7B18%7D%2C%5C%3Ax%3D%5Cfrac%7B25%5Cpi+%7D%7B18%7D%2C%5C%3Ax%3D%5Cfrac%7B29%5Cpi+%7D%7B18%7D%7D+%5C+%5Csurd)
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![c) \\ \\ sen \left(x\right)\left(2-sen \left(x\right)\right)=\cos \left(2x\right)\Rightarrow\:0\ \textless \ x\ \textless \ 2\pi \\ \\ sen \left(x\right)\left(2-sen \left(x\right)\right)-\cos \left(2x\right)=0 \\ \\ Usamos \ est\'a \ identidad: \\ \\ \cos \left(2x\right)=1-2sen ^2\left(x\right) \\ \\ Resolvemos \\ \\ -1+2sen ^2\left(x\right)+2sen \left(x\right)-sen ^2\left(x\right) \\ \\ Sumamos \ elementos \ similares: \\ \\ sen ^2\left(x\right)+2sen \left(x\right)-1=0 \\ \\ Sustituci\'on: \\ \\ u=sen(x) \\ c) \\ \\ sen \left(x\right)\left(2-sen \left(x\right)\right)=\cos \left(2x\right)\Rightarrow\:0\ \textless \ x\ \textless \ 2\pi \\ \\ sen \left(x\right)\left(2-sen \left(x\right)\right)-\cos \left(2x\right)=0 \\ \\ Usamos \ est\'a \ identidad: \\ \\ \cos \left(2x\right)=1-2sen ^2\left(x\right) \\ \\ Resolvemos \\ \\ -1+2sen ^2\left(x\right)+2sen \left(x\right)-sen ^2\left(x\right) \\ \\ Sumamos \ elementos \ similares: \\ \\ sen ^2\left(x\right)+2sen \left(x\right)-1=0 \\ \\ Sustituci\'on: \\ \\ u=sen(x) \\](https://tex.z-dn.net/?f=c%29+%5C%5C++%5C%5C+sen+%5Cleft%28x%5Cright%29%5Cleft%282-sen+%5Cleft%28x%5Cright%29%5Cright%29%3D%5Ccos+%5Cleft%282x%5Cright%29%5CRightarrow%5C%3A0%5C+%5Ctextless+%5C+x%5C+%5Ctextless+%5C+2%5Cpi++%5C%5C++%5C%5C+sen+%5Cleft%28x%5Cright%29%5Cleft%282-sen+%5Cleft%28x%5Cright%29%5Cright%29-%5Ccos+%5Cleft%282x%5Cright%29%3D0++%5C%5C++%5C%5C+Usamos+%5C+est%5C%27a+%5C+identidad%3A+%5C%5C++%5C%5C+%5Ccos+%5Cleft%282x%5Cright%29%3D1-2sen+%5E2%5Cleft%28x%5Cright%29+%5C%5C++%5C%5C+Resolvemos+%5C%5C+%5C%5C+-1%2B2sen+%5E2%5Cleft%28x%5Cright%29%2B2sen+%5Cleft%28x%5Cright%29-sen+%5E2%5Cleft%28x%5Cright%29+%5C%5C++%5C%5C+Sumamos+%5C+elementos+%5C+similares%3A+%5C%5C++%5C%5C+sen+%5E2%5Cleft%28x%5Cright%29%2B2sen+%5Cleft%28x%5Cright%29-1%3D0+%5C%5C++%5C%5C+Sustituci%5C%27on%3A+%5C%5C++%5C%5C+u%3Dsen%28x%29+%5C%5C+)
![Reescribimos: \\ \\ -1+u^2+2u=0 \\ \\ Utilizamos \ la \ formula \ general: \\ \\ a=1, \\ \:b=2, \\ \:c=-1 \\ \\ \quad u=\frac{-2\pm \sqrt{2^2-4\cdot \:1\left(-1\right)}}{2\cdot \:1} \\ \\ Resolvemos \ y \ nos \ queda: \\ \\ u=\sqrt{2}-1,\:u=-1-\sqrt{2} \\ \\ Volvemos \ a \ la \ original: \\ \\ sen \left(x\right)=\sqrt{2}-1 \\ \\ Entonces \\ \\ sen \left(x\right)=a\quad \Rightarrow \quad \:x=arcsen \left(a\right)+2\pi n,\:\quad \:x=\pi -arcsen \left(a\right)+2\pi n Reescribimos: \\ \\ -1+u^2+2u=0 \\ \\ Utilizamos \ la \ formula \ general: \\ \\ a=1, \\ \:b=2, \\ \:c=-1 \\ \\ \quad u=\frac{-2\pm \sqrt{2^2-4\cdot \:1\left(-1\right)}}{2\cdot \:1} \\ \\ Resolvemos \ y \ nos \ queda: \\ \\ u=\sqrt{2}-1,\:u=-1-\sqrt{2} \\ \\ Volvemos \ a \ la \ original: \\ \\ sen \left(x\right)=\sqrt{2}-1 \\ \\ Entonces \\ \\ sen \left(x\right)=a\quad \Rightarrow \quad \:x=arcsen \left(a\right)+2\pi n,\:\quad \:x=\pi -arcsen \left(a\right)+2\pi n](https://tex.z-dn.net/?f=Reescribimos%3A+%5C%5C+%5C%5C+-1%2Bu%5E2%2B2u%3D0+%5C%5C++%5C%5C+Utilizamos+%5C+la+%5C+formula+%5C+general%3A++%5C%5C++%5C%5C+a%3D1%2C+%5C%5C+%5C%3Ab%3D2%2C+%5C%5C+%5C%3Ac%3D-1+%5C%5C++%5C%5C+%5Cquad+u%3D%5Cfrac%7B-2%5Cpm+%5Csqrt%7B2%5E2-4%5Ccdot+%5C%3A1%5Cleft%28-1%5Cright%29%7D%7D%7B2%5Ccdot+%5C%3A1%7D+%5C%5C++%5C%5C+Resolvemos+%5C+y+%5C+nos+%5C+queda%3A+%5C%5C++%5C%5C+u%3D%5Csqrt%7B2%7D-1%2C%5C%3Au%3D-1-%5Csqrt%7B2%7D+%5C%5C++%5C%5C+Volvemos+%5C+a+%5C+la+%5C+original%3A+%5C%5C++%5C%5C+sen+%5Cleft%28x%5Cright%29%3D%5Csqrt%7B2%7D-1+%5C%5C++%5C%5C+Entonces+%5C%5C+%5C%5C+sen+%5Cleft%28x%5Cright%29%3Da%5Cquad+%5CRightarrow+%5Cquad+%5C%3Ax%3Darcsen+%5Cleft%28a%5Cright%29%2B2%5Cpi+n%2C%5C%3A%5Cquad+%5C%3Ax%3D%5Cpi+-arcsen+%5Cleft%28a%5Cright%29%2B2%5Cpi+n++)
![Soluci\'on \\ \\ \boxed{x=\pi -arcsen \left(\sqrt{2}-1\right),\:x=arcsen \left(\sqrt{2}-1\right)} \ \surd Soluci\'on \\ \\ \boxed{x=\pi -arcsen \left(\sqrt{2}-1\right),\:x=arcsen \left(\sqrt{2}-1\right)} \ \surd](https://tex.z-dn.net/?f=Soluci%5C%27on+%5C%5C+%5C%5C+%5Cboxed%7Bx%3D%5Cpi+-arcsen+%5Cleft%28%5Csqrt%7B2%7D-1%5Cright%29%2C%5C%3Ax%3Darcsen+%5Cleft%28%5Csqrt%7B2%7D-1%5Cright%29%7D+%5C+%5Csurd)
¡Espero haberte ayudado, saludos... G.G.H!
6. a) 2cos x + 3 = 2
7. b) sen3x - 2 = -3sen3x
8. c) senx(2 - senx) = cos2x
Resolvemos:
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¡Espero haberte ayudado, saludos... G.G.H!
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