Question:hard

Let \(f(x) = x^3 - 3x^2 + 2\) be a function defined on \((-1, 3]\).

Which of the following statements is/are correct?

Show Hint

Find the critical points with the first derivative, classify them with the second derivative, and do not forget to check the domain endpoints.
Updated On: Jul 22, 2026
  • \(f(x)\) has exactly two roots in \([-0.9, 0]\).
  • \(f(x)\) has a minimum at 2 only.
  • \(f(x)\) has maximum at 0 only.
  • \(f(x)\) has a root at 1.
Show Solution

The Correct Option is B, D

Solution and Explanation

Work with a value table for $f(x) = x^3 - 3x^2 + 2$ rather than pure algebra, it makes the true/false checks easier to see.

First locate where the slope is zero: $f'(x) = 3x^2 - 6x = 3x(x-2)$, zero at $x = 0$ and $x = 2$, both inside the domain $(-1, 3]$.

Build a small table of values around the interesting points:

x-1 (excluded)-0.9-0.7320122.7323
f(x)-2 (limit only)-1.159020-202

Reading the sign changes: $f$ crosses zero once between $-0.9$ and $0$ (at $x \approx -0.732$), again at $x=1$, and again at $x \approx 2.732$. Only the first crossing sits inside $[-0.9, 0]$, so there is exactly one root there, not two. Statement (A) is false.

The table also shows $f$ rising from $-1.159$ up to $f(0)=2$ (a local peak), falling back down to $f(2)=-2$ (a local trough), then climbing again to $f(3)=2$.

Since $x=-1$ is not part of the domain, the value $-2$ that $f$ would take there is never actually reached at that end. The only point where $f$ genuinely equals $-2$ in this domain is $x=2$. So statement (B), "minimum at 2 only", holds.

The peak value $2$ appears twice in the table though, once at $x=0$ and again at $x=3$, since $x=3$ is included in the domain. So the maximum is not exclusive to $x=0$, which makes statement (C) false.

The table confirms $f(1) = 0$ directly, so statement (D) is true.

So the correct statements are (B) and (D).

\[ \boxed{\text{(B) and (D)}} \]
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