Does It Always Hold?
Algebra
Level
3
\[ \begin{array} {r c r c l }
1 &\times & 1 & = &1 \\
11 & \times& 11 & = &121 \\
111 & \times& 111 & =& 12321 \\
1111 & \times& 1111 & =& 1234321 \\
\end{array} \]
Observe the equations above.
Hence, what is the value of
\[ \underbrace{1111111111}_{10 \text{ 1's } } \times \underbrace{1111111111}_{10 \text{ 1's } } \; ?\]
by
Calvin Lin