Câu hỏi 117
Chứng minh cho số nguyên $n$ rằng
$$
\left\lfloor\frac{n}{2}\right\rfloor\left\lfloor\frac{n+1}{2}\right\rfloor=\left\lfloor\frac{n^{2}}{4}\right\rfloor .
$$
$$
\left\lfloor\frac{n}{2}\right\rfloor\left\lfloor\frac{n+1}{2}\right\rfloor=\left\lfloor\frac{n^{2}}{4}\right\rfloor .
$$