Write a program to simulate the random variables whose densities are given by the following, making a suitable bar graph of each and comparing the exact density with the bar graph.

• [math]f_X(x) = e^{-x}\ \ \mbox{on}\,\, [0,\infty)\,\, (\mbox{but\,\,just\,\,do\,\,it\,\,on\,\,} [0,10]).[/math]
• [math]f_X(x) = 2x\ \ \mbox{on}\,\, [0,1].[/math]
• [math]f_X(x) = 3x^2\ \ \mbox{on}\,\, [0,1].[/math]
• [math]f_X(x) = 4|x - 1/2|\ \ \mbox{on}\,\, [0,1].[/math]