Equation $8-21$ was derived by taking the derivative of Equation $8-19,$ setting this to zero and solving for

xm$,$ the maximum rate. Perform the same procedure on Equation $8-20,$ which applies for small values of B$.$

Example $8-2$ determines a value of xm using the exact Equation $8-21.$ Compute xm using the equation derived

for this problem and compare to the more detailed result. What is the percentage error?