MonotonicityHard
Question
The function f(x) = x3 + 5x2 - 1 is decreasing in the interval-
Options
A.-
< x < 0
B.-3 < x < 3
C.0 < x < ∞
D.- ∞ < x < - 
Solution
f(x) = x3 + 5x2 - 1 f′(x) < 0
3x2 + 10x < 0
x (3x + 10) < 0

3x2 + 10x < 0
x (3x + 10) < 0

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