Rhombus is parallelogram with equal sides. The perimeter rhombus: p = 4a. The are of a rhombus: A = ah; A = a^2sinα; A = e * f / 2. The angles in a rhombus: α + β = 180°. The diagonals in a rhombus. The diagonals in a rhombus intersection at a right angle. The point of intersection divides diagonals into equal parts.