MonotonicityMedium

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      

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