Trigonometry's power

Geometry Level 4

{ log ( 192 cos x ) ( 192 sin x ) = 4 5 y = 32 ( cot 4 x 1 ) \large \begin{cases}\log_{(192\cos{x})}(192\sin{x}) =\dfrac{4}{5} \\ y = 32(\cot^{4}x-1) \end{cases}

Let x x ( 0 x π 0\leq x\leq\pi ) and y y be positive real numbers satisfying the system of equations above, enter your answer as the value of y y .


The answer is 2016.

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1 solution

Tommy Li
Jun 23, 2016

log ( 192 cos x ) 192 sin x = 4 5 \log_{(192\cos{x})}192\sin{x}=\dfrac{4}{5}

192 sin x = ( 192 cos x ) 4 5 192\sin{x}=(192\cos{x})^{\frac{4}{5}}

192 sin x = 192 cos x ( 192 cos x ) 1 5 192\sin{x}=\dfrac{192\cos{x}}{(192\cos{x})^{\frac{1}{5}}}

( 192 cos x ) 1 5 = 192 cos x 192 sin x (192\cos{x})^{\frac{1}{5}}=\dfrac{192\cos{x}}{192\sin{x}}

( 192 cos x ) 1 5 = cot x (192\cos{x})^{\frac{1}{5}}= \cot x

( 192 cos x ) 4 5 = cot 4 x (192\cos{x})^{\frac{4}{5}}= \cot^{4}x

192 sin x = cot 4 x 192\sin{x}= \cot^{4}x

192 sin x = cos 4 x sin 4 x 192\sin{x}= \dfrac{\cos^{4}x}{\sin^{4}x}

192 sin 5 x = cos 4 x 192\sin^{5}{x}= \cos^{4}x

192 sin 5 x = ( 1 sin 2 x ) 2 192\sin^{5}{x}= (1-\sin^{2}x)^{2}

192 sin 5 x ( 1 sin 2 x ) 2 = 0 192\sin^{5}{x}-(1-\sin^{2}x)^{2} =0

( 3 sin x 1 ) ( 64 sin 4 x + 21 sin 3 x + 7 sin 2 x + 3 sin x + 1 ) = 0 (3\sin x-1)(64\sin^{4}x+21\sin^{3}x+7\sin^{2}x+3\sin x+1)=0

3 sin x 1 = 0 \Rightarrow 3\sin x-1 =0

sin x = 1 3 \Rightarrow \sin x = \frac{1}{3}


cot 4 x = 192 ( 1 3 ) = 64 \cot^{4}x= 192(\frac{1}{3})=64

y = 32 ( cot 4 x 1 ) = 32 ( 64 1 ) = 2016 y=32(\cot^{4}x-1)=32(64-1)=2016

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