1. The problem statement, all variables and given/known data As shown in attachment a steel cable is stretched between two poles. In 20°C temperature the cable remains horizontal (the length of the cable 10m). At a higher temperature θ°C the cable bends like in attachment. The lamp hanging from the mid-point could be thought as weightless. The linear expansion coefficient for steel is 12 * 10^-6. What is the value of θ? 2. Relevant equations l' = l [1 + αθ] ------- 1 3. The attempt at a solution I first used pythagorian to find the expanded length so, L^2 = 25 + 64 * 10^-4 that gives L = 5.0064 so the total expanded length 2L = 10.0128 And applying it to the (1) equation I get a value for θ = 126 °C !!! obviously absurd. So anyone got a hint on what i'm doing wrong?