In a rhombus inscribed in a circle, the diagonals are equal in length and are diameters of the circle.
Therefore, the length of the other diagonal is also D.
\(\text{Area of a rhombus} = \frac{\text{diagonal}_1 \times \text{diagonal}_2}{2}\)
In this case, \(\text{Area} = \frac{D \times D}{2} = \frac{D^2}{2}\)
So, the area of the rhombus is \(\frac{D^2}{2}\)
Hence, the correct answer is (b) \(\frac{RD}{2}\)
