Step 1: {Find the maximum area of the rectangle}
The diagonal of the rectangle inscribed in the circle is equal to the diameter \( R \), so the diagonal \( d = R \).
The maximum area of the rectangle is given by:
\[
{Max Area} = \frac{1}{2} \times d_1 \times d_2 = \frac{1}{2} \times R \times R = \frac{R^2}{2}.
\]