A 30-60-90 right triangle
Acute
Equilateral triangles.
Right Triangles
congruent means that all the sides are the same length. the sides of a square have to be the same length or else it would be a rectangle. Not all triangles are congruent though. there are other types of triangles unlike the square, where there is only one type.
That is one type of pyramid.
Acute
That will depend on what type of triangle it is as for example if it is an isosceles triangle then it will form two congruent right angle triangles.
Two right angle triangles, normally scalene triangles. However, if the rectangle is for example a square, then it would be two isosceles triangles.
Equilateral triangle
Generally a parallelogram will be split into two scalene triangles by a diagonal; depending upon which diagonal, they will be acute or obtuse. However, it is possible for the diagonal to be the same length as one of the sides, in which case it will be split into two isosceles triangles. For the special case of the "regular" parallelogram (whereby every side is equal in length, and it is otherwise known as a Rhombus) it will generally be split into two isosceles triangles, but the diagonal could be the same length as the sides and it will be split into two equilateral triangles.
Equilateral triangles.
Right Triangles
congruent means that all the sides are the same length. the sides of a square have to be the same length or else it would be a rectangle. Not all triangles are congruent though. there are other types of triangles unlike the square, where there is only one type.
That is one type of pyramid.
90 degree triangles are always similar.
Equilateral triangles have rotational symmetry.
an equiangular triangle (and by definition, equilateral triangles are always equiangular too)