Δ l = α l_{0} Δ t = 12 \cdot 10^{- 6} \cdot 1000 \cdot (20^{\circ} C - (- 30^{\circ} C)) = 0, 6 m

${\Delta l = \alpha l_0\Delta t = {12\cdot 10^{-6}}{} \cdot {1000}{}\cdot ({20}\,\mathrm{^{\circ}C} -({-30}\,\mathrm{^{\circ}C}))= {0,6}\,\mathrm{m}}$