Answer:
[tex] \huge \purple { \boxed{\therefore \: \cos \: y = \frac{d}{c} }}[/tex]
Step-by-step explanation:
[tex] \because \: \tan \: y = \frac{ \sin \: y}{ \cos \: y} \\ \\ \therefore \: \cos \: y = \frac{ \sin \: y}{ \tan \: y} \\ \\ \therefore \: \cos \: y = \frac{ \frac{9}{c} }{ \frac{9}{d} } \\ \\ \therefore \: \cos \: y = \frac{9}{c} \times \frac{d}{9} \\ \\ \huge \red{ \boxed{\therefore \: \cos \: y = \frac{d}{c} }}[/tex]
