Cho ΔABC (góc A = 90°), AH ⊥ BC, HD ⊥ AB, HE ⊥ AC. Chứng minh AH^3 = BD.CE.BC

Cho ΔABC (góc A = 90°) ,AH ⊥ BC , HD ⊥ AB , HE ⊥ AC
a, Cm AH^3 =BD.CE.BC
B,Cm BC^3 = 3AH^2 + BD^2 + CE^2