a, Ta có:
$\dfrac{AB}{AC} = \dfrac{AD}{AE}$
$\dfrac{4}{5} = \dfrac{2}{AE}$
$AE = \dfrac{5}{2} = 2.5$ cm

b, Ta có:
$\dfrac{BD}{CE} = \dfrac{AB}{AC} = \dfrac{4}{5}$
$\dfrac{BD}{CE} = \dfrac{4}{5}$
$\dfrac{BD}{BD+DE} = \dfrac{4}{5}$
$5BD = 4BD + 4DE$
$BD = 4DE$

c, Ta có:
$\angle EDH = \angle ADE = \angle ABC = \angle BCH$