a)
AB= BC/2=>BC =2AB= 2×4√3 =8√3 cm
In ∆ABC dr =>T P
AB² +AC² =BC²
(4√2)+AC² =(8√3)²
AC² =(8√3)²-(4√3)²
AC² =64×3-16×3
AC² =192-48
AC² =144
AC=√144
Ac=12 cm
b)
In ∆ABC dr=>T cat
AB² =BD×BC
(4√3)²=BD ×8√3
48=BD×8√3
BD= 48/8√3
BD= 6√3
BD= 2√3 cm
BC = BD+CD=>CD=BC-BD= 8√3-2√3= 6√3 cm