a)t/ giac ABC vg tai A , AH vg goc vs BC , theo dl 2 ( he thuc giua canh va dg cao trong t /g vg) ta co : AH^2=BH.HC =>AH^2=4.9=>AH=6
theo gt co DH vg goc vs AB => goc D = 90*
___HE________AC_______E____
tu giac AEHD co : goc A =goc E =goc D =90* => AEHD la hcn => AH=DE=6 ( t/c...