An octahedron.
square
If you have 2 EQUILATERAL triangles, and you stack them on their respective hypotenuses, the result: SQUARE. If you have 2 ISOSCELES triangles, and you stack them on their respective hypotenuses, the result: RECTANGLE. If you have 2 OBTUSE triangles, and you stack them on their respective hypotenuses, the result: PARALLELOGRAM.
Any two triangles which are a mirror image of each other will form a kite if their long sides are brought together.
There is no shape that is made up 3 sides that is not a triangle. Any shape that is made up of 3 sides is classified as a triangle no matter what shape or size it is.
Scalene triangles, rectangles, rhombi, concave polygons with 5 or more sides.
A square, a cube, a diamond, a equilateral triangle, a triangular based pyramid made of equilateral triangles...
A Rhombus. If it makes two equilateral triangles with a diagonal, the shape must have all four sides of equal length; thus it is a rhombus, possibly a square. As an equilateral triangle is made, the angle between two of the sides is 60o; which is not 90o, so it can't be a square, so it must be a rhombus.
square
It would depend on the triangles, but assuming they were equilateral or isosceles, a trapezoid if alternated in a line.
The Great Pyramids at Giza are, but the Meso-Americans were truncated.
A heptagon is a shape with 7 sides. A regular heptagon is the normal version you will see however an irregular heptagon is any shape with 7 sides.To see it visually, use the triangles to create a normal hexagon (6 sides), remove one of the triangles and put it next to one of the edges near the gap.If done correctly this will create a 7 sided object - an irregular heptagon.
It is a tetrahedron
Rohmbus is a four sided figure (quadrilateral) that is made up of two equilateral triangles
If you have 2 EQUILATERAL triangles, and you stack them on their respective hypotenuses, the result: SQUARE. If you have 2 ISOSCELES triangles, and you stack them on their respective hypotenuses, the result: RECTANGLE. If you have 2 OBTUSE triangles, and you stack them on their respective hypotenuses, the result: PARALLELOGRAM.
Depending on their shapes and sizes you can make plane shapes with 3 to 24 sides.
It doesn't exist. The least number of sides for a 3-D shape only made of triangles is 4.
A triangle is a tri-angle. A shape made up of 3 sides and 3 angles.