A regular polygon must have all sides of equal length. Also, all angles must be the same measure. This applies to the equilateral triangle in the upper left corner, and the square in the upper right corner. Each angle of the square is 90 degrees even though your teacher didn't use right angle markers.
The middle figure in the top row is not a regular polygon because the sides are not all the same length. Also, the angles are different.
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In the bottom row, only the first figure is a regular polygon for similar reasons mentioned earlier. The second figure is not a regular polygon because this figure is concave. Only convex polygons can be regular.
The third figure in the bottom row is not regular because one side is longer than the others.
