xet Δ ABC va ΔABH CO
∠B chung
∠BHA=∠BAC (=90 do)
⇒ΔABC dong dang ΔABH
dua vao dinh ly py-ta-go ta co
BC²=ab²-ac²
=6²+8²=100
√100=10
VAY BC=10CM
viΔabc dong dang Δabh nen ta co
$\frac{ab}{ab}$ =$\frac{ac}{ah}$
thay so ta co $\frac{6}{6}$ =$\frac{8}{ah}$
⇒ah=$\frac{8.6}{6}$
= 8cm
vay ah = 8cm
⇒ bc.hc.$\frac{8}{2}$
=$\frac{10}{8}$ .$\frac{8}{2}$
=80:16=5
