When \(T _1=100\,N\), Extension \(=\ell_1-\ell_0\)
When \(T _2=120\,N\), Extension \(=\ell_2-\ell_0\)
Then \(100= K \left(\ell_1-\ell_0\right)\)
And \(120= K \left(\ell_2-\ell_0\right)\)
\(\frac{1}{2} \Rightarrow \frac{5}{6}=\frac{\ell_1-\ell_0}{\ell_2-\ell_0}\)
\(5 \ell_2-5 \ell_0=6 \ell_1-6 \ell_0\)
\(\ell_0=6 \ell_1-5 \ell_2\)
\(\ell_0=6 \ell_1-5\left(\frac{11 \ell_1}{10}\right)\)
\(\ell_0=6 \ell_1-\frac{11 \ell_1}{2}\)
\(\ell_0=\frac{\ell_1}{2}\)
\(\therefore x=2\)