Vì AD là phân giác nên \(\dfrac{AB}{AC}=\dfrac{DB}{DC}\Rightarrow\dfrac{AB}{DB}=\dfrac{AC}{DC}\Rightarrow\left(\dfrac{AB}{DB}\right)^2=\left(\dfrac{AC}{DC}\right)^2\)
Theo tc dãy tỉ số bằng nhau
\(\left(\dfrac{AB}{DB}\right)^2=\left(\dfrac{AC}{DC}\right)^2=\dfrac{AB^2+AC^2}{DB^2+DC^2}=\dfrac{1225}{625}=\dfrac{49}{25}\)
\(\Rightarrow AB=21cm;AC=28cm\)