A composite bar made from two different materials of equal cross-sectional areas are directly attached to each other making the bar a length of L = L1 + L2.The coefficient of thermal expansion for the two materials are x1 and x2 respectively. Assume the cross-section of each bar is unaffected by the heating and determine the effective coefficient of linear expansion for the composite bar x in terms of L1, L2, x1,and x2.