A 3 sided shape is a triangle. A 4 sided shape could be a square or rectangle.
A 3-sided shape is called a triangle.or Polygon in general.
it is called a seven sided shape in Canada
a one sided shape is called a henagon and a 2 sided shape is called a digon
it is called a triangle
a polyhedron (if the shape is 3 dimensional) a polygon if it is a planar shape.
Typically this is called a triangle. :)
A 10-sided shape is called a decagon.