8. Find the radius of convergence of the power series

7. The production for a certain country in the early years following World War II is described by the function f(x, y) =units, when ; units of labor and y units of capital were utilized. Find the approximate change in output if the amount expended on labor had been decreased from 125 units to 123 units and the amount expended on capital had been increased from 27 to 29 units.