Question:medium

The function $f(x)=[x(x-2)]^{2}$ is increasing in the set}

Show Hint

Use the wavy curve method for inequalities involving polynomial derivatives.
Updated On: Jun 19, 2026
  • $(-\infty,0)\cup(2,\infty)$
  • $(-\infty,1)$
  • $(1,2)$
  • $(0,1) \cup(2,\infty)$
Show Solution

The Correct Option is D

Solution and Explanation

Step 1: Understanding the Question:
A function is increasing where its derivative $f'(x) > 0$.

Step 3: Detailed Explanation:

$f(x) = (x^2 - 2x)^2$
$f'(x) = 2(x^2 - 2x) \cdot \frac{d}{dx}(x^2 - 2x)$
$f'(x) = 2(x(x-2))(2x-2) = 4x(x-2)(x-1)$
Find roots of $f'(x)$: $x = 0, 1, 2$.
Using sign scheme (Wavy curve method):
- For $x > 2$, $f'(x)$ is $(+)(+)(+) = +$. (Increasing)
- For $1 < x < 2$, $f'(x)$ is $(+)(-)(+) = -$. (Decreasing)
- For $0 < x < 1$, $f'(x)$ is $(+)(-)(-) = +$. (Increasing)
- For $x < 0$, $f'(x)$ is $(-)(-)(-) = -$. (Decreasing)
Increasing intervals: $(0, 1) \cup (2, \infty)$.

Step 4: Final Answer:

The function is increasing on $(0, 1) \cup (2, \infty)$.
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