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The interval in which the function f(x)=10−6x−2x2f(x) = 10 - 6x - 2x^2 is decreasing is :

Solution

✅ Correct Option: 3

f′(x)=−6−4xf'(x) = -6 - 4x.

For decreasing: f′(x)<0⇒−6−4x<0⇒x>−32f'(x) < 0 \Rightarrow -6 - 4x < 0 \Rightarrow x > -\frac{3}{2}.

So ff is decreasing on (−32,∞)\left(-\frac{3}{2}, \infty\right).

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