Chamfering formula and included angle formula have their own advantages and disadvantages, and another problem is the existence of slope (of course, this problem need not be considered, because it refers to finding slope), let k, and then | k-k1| |1+kk1| = | k-k2 |/kloc-0. Write k-k11+kk1= k-k2/1+kk2 or k-k1/(1+kk1)+.