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The interval in which f(x)=−2x3−9x2−12x+1f(x)=-2x^3-9x^2-12x+1 is increasing, is:

Solution

✅ Correct Option: 3

f′(x)=−6x2−18x−12=−6(x+1)(x+2)f'(x)=-6x^2-18x-12=-6(x+1)(x+2).

This is positive exactly when (x+1)(x+2)<0(x+1)(x+2)<0, i.e. for −2<x<−1-2<x<-1.

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