In Problems 69-76, apply steps 1-3 of the graphing strategy to f(x). Use a graphing calculator to approximate (to two decimal places) x intercepts, critical values, and x coordinates of inflection points. Summarize all the pertinent information.
70. f(x) = x4 + 2x3 - 5x2 - 4x + 4
72. f(x) = x4 - 12x3 + 28x2 + 76x - 50
74. f(x) = -x4 + x3 + x2 + 6
76. f(x) = x5 + 4x4 - 7x3 - 20x2 + 20x - 20