Вопрос:

Ответ:

\[x_{n} = n(n - 1)\]

\[x_{2} = 2 \cdot (2 - 1) = 2;\]

\[x_{5} = 5 \cdot (5 - 1) = 20;\]

\[x_{10} = 10 \cdot (10 - 1) = 90.\]