請寬恕

首先講明唔該，唔好一大班傻仔走入黎放句：
唔識唔識／好難好難／乜野黎　等等，
唔識就咪回，左９住。

回正題：

By mathematical induction , prove that the following propositions are true for all positive integers n .

請寬恕

自推一下，等待高手。