Abstract: The serious errors of differential equation about ball games considering air resistance in some magazines are pointed out; right differential equation on condition that the air resistance is directly proportional to square of velocity and its approximate solution and the parameter equation computing the optimum putting angle of a shot are given. Meanwhile the practical equation of optimum putting angle of a shot on condition that the air resistance is directly proportional to velocity are also deduced.

Key words: changeable coefficient differential equationoptimum putting angle, practical equationgroup, approximate solution, parameter equation