A nonagon is a nine-sided polygon. If a regular nonagon was rotated about its center point, which of the following angles of rotation would not map the figure onto itself?

60
120
80
40

1 answer

To determine which angles of rotation would not map a regular nonagon onto itself, we need to consider the angles that would allow the nonagon to look the same after rotation.

A regular nonagon has 9 sides, and therefore can be rotated by multiples of \( \frac{360^\circ}{9} = 40^\circ \) to map it onto itself. This means any angle that is a multiple of 40 degrees is a valid angle of rotation that maps the nonagon onto itself.

The angles of rotation we were given are:

  • 60°
  • 120°
  • 80°
  • 40°

Now we can check each of these angles to see if they are multiples of 40°:

  1. 60°: \( 60^\circ \div 40^\circ = 1.5 \) (not a multiple)
  2. 120°: \( 120^\circ \div 40^\circ = 3 \) (multiple of 40)
  3. 80°: \( 80^\circ \div 40^\circ = 2 \) (multiple of 40)
  4. 40°: \( 40^\circ \div 40^\circ = 1 \) (multiple of 40)

From this analysis, the angle that does not map the regular nonagon onto itself is:

60°.