$(20$ points$)$ The lift$-$induced drag for a $3$ D wing with aspect ratio $AR=5$ is

$C_{D_i}=C_{D_{}}=0\mathrm{.}009$

The total drag force is given by $C_D=C_{D_{}}+C_{Di}.$

$($a$)$ What is the coefficient of lift $C_L?$

$($b$)$ What is the angle of attack $$ if $C_L=\frac{2sin}{1+\frac{2}{A}R}?$