Chu ki dao dong bang nhau khi tan so goc cua 2 dao dong bang nhau khi do:
$\frac{k_{1}}{m_{1}}=\frac{k_{2}}{m_{2}}$
$<=>\frac{k_{1}}{k_{2}}=\frac{m_{1}}{m_{2}}=0,6$
Lai co
$\frac{k_{1}}{k_{2}}=\frac{l_{2}}{l_{1}}=\frac{CB}{AC}=0,6$
$BC=0,6AC$
Mat khac $AC+CB=1m$
$<=>1,6AC=1m<=>AC=\frac{5}{8}m$