Hint:

\(\displaystyle{\tan{\phi}}={\frac{{a}}{{b}}}\)

\(\displaystyle{\frac{{{\sin{\phi}}}}{{{a}}}}={\frac{{{\cos{\phi}}}}{{{b}}}}=\pm\sqrt{{{\frac{{?}}{{{a}^{{2}}+{b}^{{2}}}}}}}\)

Now replace the values of a,b

\(\displaystyle{\tan{\phi}}={\frac{{a}}{{b}}}\)

\(\displaystyle{\frac{{{\sin{\phi}}}}{{{a}}}}={\frac{{{\cos{\phi}}}}{{{b}}}}=\pm\sqrt{{{\frac{{?}}{{{a}^{{2}}+{b}^{{2}}}}}}}\)

Now replace the values of a,b