\(T_1=2\pi \sqrt{\frac{m}{k_1}}\Rightarrow \frac{1}{k_1}=\frac{T_1^2}{4\pi ^2m}\)

\(T_2=2\pi \sqrt{\frac{m}{k_2}}\Rightarrow \frac{1}{k_2}=\frac{T_2^2}{4\pi ^2m}\)

\(T_n=2\pi \sqrt{\frac{m}{k_n}}\Rightarrow \frac{1}{k_n}=\frac{T_n^2}{4\pi ^2m}\)

Mắc nối tiếp \(\frac{1}{k}=\frac{1}{k_1}+\frac{1}{k_2}+...+\frac{1}{k_n}\)

\(\Rightarrow \frac{T^2}{4\pi ^2m}=\frac{T_1^2}{4\pi ^2m}+\frac{T_2^2}{4\pi ^2m}+...+\frac{T_n^2}{4\pi ^2m}\Rightarrow T^2=T_1^2+T_2^2+...+T_n^2\)