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ID:
Class: 12
Subject: Math
Topic: Application of Derivative
Type: Short
Question:
Find the intervals in which the function \(f(x) = 6 - 9x - x^2\) is strictly increasing or strictly decreasing.
Official Solution
Explanation:
We have:
\[f'(x) = -9 - 2x\]
Setting \(f'(x) = 0\):
\[x = -\dfrac{9}{2}\]
In \(\left(-\infty, -\dfrac{9}{2}\right)\), \(f'(x) > 0\) ⟹ strictly increasing
\[\]
In \(\left(-\dfrac{9}{2}, \infty\right)\), \(f'(x) < 0\) ⟹ strictly decreasing
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