You could call them a pair of additive inverses.
They are additive inverses of each other. They are often called opposites, but that is not good practise. You can have multiplicative inverses (1/2 and 2 because they multiply to 1), and will you call them opposites also?
a rhombus
Parallelogram
A parallelogram.
It is called Perimeter. For example if you have a square with 10 on all 4 sides, the distance or perimeter of the sides is 40
the radius
A kite or a parallelogram, depending on whether the equal sides are adjacent to, or opposite one another.
It's called a "full moon", or if they are TRULY opposite each other, it's an eclipse.
A parallelogram. Example of parallelogram is a square, a rectangle, and a rhombus.
A quadrilateral is a polygon with 4 sides. ... Definition: A parallelogram is a quadrilateral where both pairs of opposite sides are parallel. We use the symbol to represent a parallelogram.
Positive integers, if I understood you correctly
In Euclidean geometry, a parallelogram is a simple (non self-intersecting) quadrilateral with two pairs of parallel sides. The opposite or facing sides of a parallelogram are of equal length and the opposite angles of a parallelogram are of equal measure. The congruence of opposite sides and opposite angles is a direct consequence of the Euclidean Parallel Postulate and neither condition can be proven without appealing to the Euclidean Parallel Postulate or one of its equivalent formulations.A simple (non self-intersecting) quadrilateral is a parallelogram if and only if any one of the following statements is true;Two pairs of opposite sides are equal in lengthOne pair of opposite sides are parallel and equal in length.source:From Wikipedia, the free encyclopedia;Subject: Parallelogram.