Which property is true of a rhombus?

A rhombus is a type of polygon that is a special case of a parallelogram. The defining characteristic of a rhombus is that it has all four sides equal in length. In addition to this, opposite angles are equal, which is a property that distinguishes rhombuses from other polygons. This means that if you know the length of one side, you can conclude that all sides are of that same length.

Moreover, while a rhombus may not have right angles (90 degrees) like a square does, it always maintains the property that opposite angles are equal. This means if one angle measures (30^\circ), the opposite angle also measures (30^\circ), while the adjacent angles would measure (150^\circ).

The other properties described in the other options do not apply to rhombuses. For example, a rhombus is not defined as having all angles equal to 90 degrees, nor is it a type of triangle. Furthermore, the diagonals of a rhombus actually bisect each other at right angles, and while the diagonals are unequal in a rhombus, this is a general property of all rhombuses, and they are not necessarily the same length.