A triangle
A 3-sided figure is called a triangle.
In 2 dimensions, a regular 5 sided figure is a pentagon. In 3 dimensions, there is no regular sided 5 sided figure. The tetrahedron is a regular 4 sided figure and a cube is a regular 6 sided figure.
a 3 sided figure
A 5-sided figure can be drawn with any area that anybody wants.
There cannot be a solid three sided figure. A solid 4 sided object is a tetrahedron.
Triangle
It is any 4 sided figure.
no
a square or rectangle
An acute triangle.
a triangle, a 3 sided figure, a figure with 3 points, etc.
heptagon * * * * * No. That is a 7 sided figure. A 17 sided figure is a heptadecagon.