[tex]x = 4 \cos(a) [/tex]
[tex] \frac{x}{4} = \cos(a) \\ [/tex]
[tex]( { \frac{x}{4} })^{2} = ({ \cos(a) })^{2} \\ [/tex]
[tex] \frac{ {x}^{2} }{16} = {cos}^{2} (a) \\ [/tex]
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[tex]y = 5 \tan(a) [/tex]
[tex] \frac{y}{5} = \tan(a) \\ [/tex]
[tex]( { \frac{y}{5} })^{2} = ( { \tan(a) })^{2} \\ [/tex]
[tex] \frac{ {y}^{2} }{25} = {tan}^{2} (a) \\ [/tex]
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Thus ;
[tex] \frac{ {x}^{2} }{16} - \frac{ {y}^{2} }{25} = \\ [/tex]
[tex] {cos}^{2} (a) - {tan}^{2} (a)[/tex]
