Area of a rhombus

A rhombus is a parallelogram, so its area is S = a · h, where a is a side and h is the altitude drawn to it. The diagonals of a rhombus are perpendicular and bisect each other at their intersection point, so the rhombus splits into four congruent right triangles. The legs of each triangle are d₁ : 2 and d₂ : 2, so the four triangles have total area 4 · (d₁/2 · d₂/2 : 2) = d₁ · d₂ : 2. Hence S = d₁ · d₂ : 2: the area of a rhombus is half the product of its diagonals. Choose one of the two formulas according to which quantities the problem gives.