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 #1
avatar+4619 
0
Aug 12, 2016
 #1
avatar+12531 
0
Aug 12, 2016
 #2
avatar+26388 
0

2sec(x+60)=5sec(x-20)

 

\(\begin{array}{|rcll|} \hline 2\cdot \sec(x+60^{\circ}) &=& 5\cdot \sec(x-20^{\circ}) \\ \text{We substitute } x = y-20^{\circ} \\\\ 2\cdot \sec(y-20^{\circ}+60^{\circ}) &=& 5\cdot \sec(y-20^{\circ}-20^{\circ}) \\ 2\cdot \sec(y+40^{\circ}) &=& 5\cdot \sec(y-40^{\circ}) \quad | \quad \sec(\phi) = \frac{1}{\cos(\phi)}\\ \frac{ 2 } { \cos(y+40^{\circ}) } &=& \frac{ 5 } { \cos(y-40^{\circ}) } \\ \frac{ \cos(y-40^{\circ}) } { \cos(y+40^{\circ}) } &=& \frac{ 5 } { 2 } \quad | \quad \cos(y-40^{\circ}) = \cos(y)\cos(40^{\circ})+\sin(y)\sin(40^{\circ}) \\ \frac{ \cos(y)\cos(40^{\circ})+\sin(y)\sin(40^{\circ}) } { \cos(y+40^{\circ}) } &=& \frac{ 5 } { 2 } \quad | \quad \cos(y+40^{\circ}) = \cos(y)\cos(40^{\circ})-\sin(y)\sin(40^{\circ}) \\ \frac{ \frac{\cos(y)\cos(40^{\circ})+\sin(y)\sin(40^{\circ})} {\cos(y)\cos(40^{\circ})} } { \frac{\cos(y)\cos(40^{\circ})-\sin(y)\sin(40^{\circ})} {\cos(y)\cos(40^{\circ})} } &=& \frac{ 5 } { 2 } \\ \frac{ 1+\tan(y)\tan(40^{\circ}) } {1-\tan(y)\tan(40^{\circ}) } &=& \frac{ 5 } { 2 } \\\\ 2\cdot [~ 1+\tan(y)\tan(40^{\circ}) ~] &=& 5\cdot [~ 1-\tan(y)\tan(40^{\circ}) ~] \\ 2 + 2\cdot \tan(y)\tan(40^{\circ}) &=& 5 - 5 \cdot \tan(y)\tan(40^{\circ}) \\ 7\cdot \tan(y)\tan(40^{\circ}) &=& 3 \\ \tan(y) &=& \frac37\cdot \frac{1}{\tan(40^{\circ})} \quad | \quad y=x+20^{\circ}\\ \tan(x+20^{\circ}) &=& \frac37\cdot \frac{1}{\tan(40^{\circ})} \\ x+20^{\circ} &=& \arctan{\left( \frac37\cdot \frac{1}{\tan(40^{\circ})} \right)} \pm n\cdot 180^{\circ}\\ x &=& -20^{\circ} + \arctan{\left( \frac37\cdot \frac{1}{\tan(40^{\circ})} \right)} \pm n\cdot 180^{\circ}\\ x &=& -20^{\circ} + \arctan{\left( 0.51075153968 \right)} \pm n\cdot 180^{\circ}\\ x &=& -20^{\circ} + 27.0557431286^{\circ} \pm n\cdot 180^{\circ}\\\\ \mathbf{x} &\mathbf{=}& \mathbf{7.0557431286^{\circ} \pm n\cdot 180^{\circ} } \qquad n \in N\\ \hline \end{array}\)

 

laugh

Aug 12, 2016
 #1
avatar+26388 
+1

If log_(8)3=P and log_(3)5=Q, express log_(10)5 in terms of P and Q.

Your answer should no longer include any logarithms.

 

\(\begin{array}{|rcll|} \hline \log _b \left( x \right) &=& \dfrac{ \log _c \left( x \right) } { \log _c \left( b \right) } \\ \hline \end{array}\)

 

\(\begin{array}{|rcll|} \hline &P &=& \log_8 \left( 3 \right) \\\\ &P &=& \dfrac{ \log _{10} \left( 3 \right) } { \log _{10} \left( 8 \right) } \\\\ &P &=& \dfrac{ \log _{10} \left( 3 \right) } { \log _{10} \left( 2^3 \right) } \\\\ &P &=& \dfrac{ \log _{10} \left( 3 \right) } { 3\cdot \log _{10} \left( 2 \right) } \\ \hline (1) & \log _{10} \left( 2 \right) &=& \dfrac{ \log _{10} \left( 3 \right) } {3P} \\ \hline \end{array} \)

 

\(\begin{array}{|rcll|} \hline &Q &=& \log_3 \left( 5 \right) \\\\ &Q &=& \dfrac{ \log _{10} \left( 5 \right) } { \log _{10} \left( 3 \right) } \\\\ \hline (2) & \log _{10} \left( 3 \right) &=& \dfrac{ \log _{10} \left( 5 \right) } {Q} \\ \hline \end{array} \)

 

\(\begin{array}{|rcll|} \hline \log _{10} \left( 5 \right) &=& \log _{10} \left( \frac{10}{2} \right) \\\\ \log _{10} \left( 5 \right) &=& \log _{10} \left( 10 \right)- \log _{10} \left( 2 \right) \quad &| \quad \log _{10} \left( 10 \right) = 1\\\\ \log _{10} \left( 5 \right) &=& 1- \log _{10} \left( 2 \right) \quad &| \quad \log _{10} \left( 2 \right) = \dfrac{ \log _{10} \left( 3 \right) } {3P}\\\\ \log _{10} \left( 5 \right) &=& 1- \dfrac{ \log _{10} \left( 3 \right) } {3P} \quad &| \quad \log _{10} \left( 3 \right) = \dfrac{ \log _{10} \left( 5 \right) } {Q}\\\\ \log _{10} \left( 5 \right) &=& 1- \dfrac{ \dfrac{ \log _{10} \left( 5 \right) } {Q} } {3P} \\\\ \log _{10} \left( 5 \right) &=& 1- \dfrac{ \log _{10} \left( 5 \right) } {3PQ} \\\\ \log _{10} \left( 5 \right) + \dfrac{ \log _{10} \left( 5 \right) } {3PQ} &=& 1 \\\\ \log _{10} \left( 5 \right)\cdot \left( 1+ \dfrac{ 1 } {3PQ} \right ) &=& 1 \\\\ \log _{10} \left( 5 \right)\cdot \left( \dfrac{ 3PQ+1 } {3PQ} \right ) &=& 1 \\\\ \mathbf{\log _{10} \left( 5 \right)} &\mathbf{=}& \mathbf{\dfrac{3PQ}{ 3PQ+1 } }\\ \hline \end{array}\)

 

laugh

Aug 12, 2016

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