I need help with defining the integral of a marginal pdf Given: $f(x,y)=1/\pi a^2,$ when $x^2+y^2\le a^2\,(a&gt;0)$
In order to find the marginal pdfs, I have to set up the integral. I don't understand how to go about it as the expression is composed of constants only.
\begin{align} 
f_x(x) &amp;= \int_{-\sqrt{a^2 -x^2}}^{\sqrt{a^2 -x^2}} f(x,y) \, dy \\
&amp;= \left(\frac{y}{\pi a^2}\right)_{-\sqrt{a^2 -x^2}}^{\sqrt{a^2 -x^2}} \\
&amp;= \frac{2\sqrt{a^2 -x^2}}{\pi a^2}
\end{align}
\begin{align} 
f_x(x) &amp;= \int_{-\sqrt{a^2 -x^2}}^{\sqrt{a^2 -x^2}} f(x,y) \, dy \\
&amp;= \left(\frac{y}{\pi a^2}\right)_{-\sqrt{a^2 -x^2}}^{\sqrt{a^2 -x^2}} \\
&amp;= \frac{2\sqrt{a^2 -x^2}}{\pi a^2}
\end{align}