\"\"

\

Let \"\" represent interior angle of a regular nonagon.

\

\"\"             (Apply interior angle formula)

\

\"\"             (Substitute \"\")

\

\"\"                   (Subtract: \"\")

\

\"\"                      (Multiply: \"\")

\

\"\"                             (Divide: \"\")\"\"

\

Since 42 is not a factor of 360,a 30-gon will not tessellate the plane.