$m(DCB)=x \\ |CD|=2 \cos{x} \\ |AD|=\dfrac{2\cos^2{x}} {\sin{x}} \\ A(ADC)= \dfrac{2 \cdot \cos{x} \cdot \dfrac{2\cos^2{x}} {\sin{x}}}2=\dfrac{2\cos^3{x}} {\sin{x}}$