Triangle
If a figure is not a triangle then it does not have three sides ,is the contrapositive of the statement given in the question.
triangle
A triangle.
That is a triangle.
That is a triangle.
A polygon is formed by three or more sides. there is no specific figure.
A triangle
A triangle.
Polygons have multiple sides and angles.
square
Triangle (assuming you were asking 'three sides').
A polygon.