Homework Problem 8, Due Wednesday February 20.
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(a) Write and test a function to simulate a random 
two-dimensional vector variable  (X,Y)  with joint density

f(x,y)  =  (1.5/x^2) * (1/max(x^2, y^2)) ,  for    x, y > 1,  

(b) Write an R function to generate  N independent random 
points points (X_i,Y_i)  uniformly distributed within the 
triangle which has one side equal to the segment from 
(-5,0) to (5,0) on the  x-axis and which has opposite 
vertex (1,4). Your function should be based on an 
ACCEPT/REJECT METHOD using randomly generated points in 
the rectangle  [-5,5] x [0,4].

In both parts (a) and (b), you should test the output of 
your function for appropriate behavior, in terms of histograms 
versus (marginal) densities, of various theoretical versus 
simulated probabilities, and/or theoretical versus 
empirical marginal distribution functions. In particular, 
your test in (b) should confirm [persuasivley, if not 
exhaustively] that the points you generate are uniformly 
distributed in the triangle.