28. Correct. The answer is false. dAVC/dQ
= 3Q^{2}/3 - 6*2Q + 11 + 0 = Q^{2 }-12Q + 11(Use the Constant
Function, Power, and Sum-Difference Rules). Setting it equal to zero, Q^{2}
- 12Q + 11 = 0, we obtain the roots of the quadratic equation Q = 6.5 and Q =
-18.5. The latter makes no economic sense, therefore, the candidate for the
optimal level of production is Q=6.5. Checking second order conditions d^{2}AVC/dQ^{2}
= 2Q - 12. At Q = 6.5d^{2}TC/dQ^{2} = 2*6.5 - 12= 1>0. Therefore,
ATC(Q) is minimum at the optimal level 6.5.