Answer
$\frac{d\rho}{dT} = -21 \times 10^{3} \Omega . m /K$
Work Step by Step
For Silicon,
$\frac{d\rho}{dT} = [\rho\alpha]_{Si} $
Where
$\rho = 3 \times 10^{3} \Omega . m$
$\alpha = -70 \times 10^{-3} K^{-1} $
Substitute into equation
$\frac{d\rho}{dT} = (3 \times 10^{3} \Omega . m)(-70 \times 10^{-3} K^{-1} )$
$\frac{d\rho}{dT} = -21 \times 10^{3} \Omega . m /K$
