MonotonicityHard
Question
Function f(x) = x3 - 3x2 - 9x + 22 is monotonic decreasing when-
Options
A.-1 < x < 3
B.1 < x < 3
C.-3 < x < -1
D.None of these
Solution
f(x) = x3 - 3x2 - 9x + 22
f′(x) = 3x2 - 6x - 9 < 0
x2 - 2x - 3 < 0
- 1 < x < 3
f′(x) = 3x2 - 6x - 9 < 0
x2 - 2x - 3 < 0
- 1 < x < 3
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