please solve all with clear steps, for the first one use defenition of changing variables to s and t
example:
The joint pdf of (X,Y) is given by
Fxy(x,y)= x+y+1/2
for 0 < x <1,0 1. Find the cumulative distribution function of (X,Y). .
2. Find the marginal density of X. 3. Find the marginal density of Y