[tex]pr_{(ABC)}BD'=AD'=\ \textgreater \ m(\ \textless \ ((ABC),BD'))=m(\ \textless \ (BD',AD'))=\\
m(\ \textless \ BD'A).\\
BA\_|\_(ADD')\\
AD'\ inclus\ (ADD')=\ \textgreater \ BA\_|\_AD'=\ \textgreater \ \Delta BAD'\ dreptunghic\\
AD'^2=AD^2+DD'^2\\
AD'^2=288+144\\
AD'^2=432=\ \textgreater \ AD'=12\sqrt3\\
In\ \Delta AD'B:tgD'=\frac{AB}{AD'}\\
tgD'=\frac{12}{12\sqrt3}=\frac{\sqrt3}{3}=\ \textgreater \ m(\ \textless \ AD'B)=30^0[/tex]
