$\begin{align}  & \beta =3\alpha =3\times 1/7\times {{10}^{-5}}=5/1\times {{10}^{-5}}{{K}^{-1}} \\  & {{\rho }_{2}}=\frac{{{\rho }_{1}}}{1+\beta \Delta \theta }\simeq {{\rho }_{1}}(1-\beta \Delta \theta )\Rightarrow {{\rho }_{2}}-{{\rho }_{1}}=-{{\rho }_{1}}\beta \Delta \theta \Rightarrow darsad\,taghier\,chegali=\frac{\Delta \rho }{{{\rho }_{1}}}\times 100=-100\beta \Delta \theta =-100\times 5/1\times {{10}^{-5}}\times 1000=-5/1darsad\simeq 5darsad \\ \end{align}$