C}{\sin C}\]; \[\frac{5}{\sin \left( \frac{\pi }{2}+B \right)}=\frac{4}{\sin B}\] \[\frac{5}{\cos B}=\frac{4}{\sin B}\], \ \[\tan B=\frac{4}{5}\] \[\tan A=\tan \left( \frac{\pi }{2}+B \right)=-\cot B=\frac{-5}{4}\] \[\tan C=\tan (\pi -(A+B))\]\[=-\tan (A+B),\]\[[A+B+C=\pi ]\] \[=-\frac{(\tan A+\tan B)}{1-\tan A.\tan B}\]\[=\frac{-\left( -\frac{5}{4}+\frac{4}{5} \right)}{1+1}=\frac{9}{40}\] \[C={{\tan }^{-1}}\left( \frac{\left( 2.\frac{1}{9} \right)}{1-{{\left( \frac{1}{9} \right)}^{2}}} \right)\]; \ \[C=2{{\tan }^{-1}}\left( \frac{1}{9} \right)\].