To compute \( 987654321^2 \), let's break it down step by step:

\[
987654321^2 = 987654321 \times 987654321.
\]

We can perform the multiplication directly:

\[
987654321 \times 987654321 = 975460084801875721.
\]

Thus, the exact value of \( 987654321^2 \) is:

\[
\boxed{975460084801875721}.
\]
