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Question
Choose the correct option from the given alternatives :
Let f(x) = x3 – 6x2 + 9x + 18, then f(x) is strictly decreasing in ______.
Options
`(-oo, 1)`
`[3, oo)`
`(-oo, 1] ∪ [3, oo)`
(1, 3)
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Solution
Let f(x) = x3 – 6x2 + 9x + 18, then f(x) is strictly decreasing in (1, 3).
Explanation:
Here, `f(x) = 3x^2 - 12x + 9`
= `3(x - 1)(x - 3) ≤ 0 ⇔ x ∈ [1, 3]`
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