question_answer

The sum \[\underbrace{{{(666..6)}^{2}}}_{n\,digits}+\underbrace{(888..8)}_{n\,digits}\]is equal to

A) \[\frac{4}{9}{{({{10}^{n}}-1)}^{2}}\]          

B) \[\frac{4}{9}({{10}^{n}}-1)\]

C) \[\frac{4}{9}({{10}^{2n}}-1)\]

D) \[4({{10}^{n}}+1)\]