( a + b > c ), ( a + c > b ), ( b + c > a ), with equality degenerate.
A parallelogram is a rhombus iff diagonals are perpendicular or one diagonal bisects an interior angle. properties of triangles and quadrilaterals
Proof (synthetic): Through a vertex, draw a line parallel to the opposite side. Alternate interior angles give the sum of the three angles as a straight angle. ( a + b > c ), (
( a + b > c ), ( a + c > b ), ( b + c > a ), with equality degenerate.
A parallelogram is a rhombus iff diagonals are perpendicular or one diagonal bisects an interior angle.
Proof (synthetic): Through a vertex, draw a line parallel to the opposite side. Alternate interior angles give the sum of the three angles as a straight angle.