in a circle of diameter 40 cm, a rhombus is inscribed with all its vertices on the circle. Find the area of rhombus

Given   A circle of diameter 40 cm and ABCD is a rhombus inscribed in the circle and all the four vertices of the rhombus lie on the circle
Now it is clearly seen from the figure that diagonals of the rhombus are the diameter of the circle .
Hence the length of the diagonals is 40 cm
$$\begin{gathered} Area of a rhombus = \frac{1}{2}\times product of diagonals \\ \therefore Area of the given rhombus = \frac{1}{2}\times 40 cm\times 40 cm=800 c{m}^2 \end{gathered}$$