a: \(BC=\sqrt{21^2+72^2}=75\left(cm\right)\)
b: \(AH=\dfrac{21\cdot72}{75}=20.16\left(cm\right)\)
\(BH=\sqrt{21^2-20.16^2}=5.88\left(cm\right)\)
a, Áp dụng PTG: \(BC=\sqrt{AB^2+AC^2}=75\left(cm\right)\)
b, Áp dụng HTL: \(\left\{{}\begin{matrix}BH=\dfrac{AB^2}{BC}=5,88\left(cm\right)\\AH=\dfrac{AB\cdot AC}{BC}=20,16\left(cm\right)\end{matrix}\right.\)
c, Vì BD là p/g nên \(\dfrac{AD}{DH}=\dfrac{AB}{BH}=\dfrac{25}{7}\Rightarrow AD=\dfrac{25}{7}DH\)
Mà \(AD+DH=AH\Rightarrow\dfrac{32}{7}DH=20,16\Rightarrow DH=4,41\left(cm\right)\)
\(\Rightarrow AD=15,75\left(cm\right)\)
