9.假设贴现率 6%。（如果是 4%或 5%的话，差别还挺大的，谁没事算算？）响应一下号召，其实一行python就输出1% 至 10% 的结果
>>> import numpy; [ f"({r*100:.0f}%, {10*((1+r)-(1+r)**(-9))/r:.4f})" for r in numpy.arange(0.01, 0.11, 0.01)]
['(1%, 95.6602)', '(2%, 91.6224)', '(3%, 87.8611)', '(4%, 84.3533)', '(5%, 81.0782)', '(6%, 78.0169)', '(7%, 75.1523)', '(8%, 72.4689)', '(9%, 69.9525)', '(10%, 67.5902)']