Suppose (X,Y) have a uniform distribution over S, their joint PDF is given by $f_{X,Y}(x,y)=\frac{1}{16}, (x,y) \in S$.
Problem 1: find the marginal PDF $f_X(x)$ of X.
Question 1: I know f_X(x) is the integral of Y=y but how do I represent this in this diagram? $f_X(x)= \int_0^4 \frac{1}{16} dy$?