Asmokestack deposits soot on the ground with a concentration inversely proportional to the square of the distance from the stack. with two smokestacks d miles apart, the concentration of the combined deposits on the line joining them, at a distance x from one stack, is given by s=cx2+k(d−x)2 where c and k are positive constants which depend on the quantity of smoke each stack is emitting. if k=3c, find the point on the line joining the stacks where the concentration of the deposit is a minimum.
xmin =