Given, {(x, 0) :

\[\begin{array}{*{35}{l}}

y~=\text{ }\surd \left( 4\text{ }~-{{x}^{2}} \right)\  \\

So,\text{ }{{y}^{2}}~=\text{ }4\text{ }-\text{ }{{x}^{2}}  \\

{{x}^{2}}~+\text{ }{{y}^{2}}~=\text{ }4  \\

\end{array}\]

which is a circle.

Now, the required area