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Let f:R→Rf: \mathbb{R} \to \mathbb{R} be a function such that

f′(x)=(x−2024)3(x−2025)(x−2026)2f'(x) = (x - 2024)^3(x - 2025)(x - 2026)^2 for all x∈Rx \in \mathbb{R}.

Let g:R→(0,∞)g: \mathbb{R} \to (0, \infty) be a function such that g(x)=f(x)g(x) = \sqrt{f(x)} for all x∈Rx \in \mathbb{R}.

Then the number of points at which g(x)g(x) has a local maximum is:

Solution

✅ Correct Option: 2

Given f′(x)=(x−2024)3(x−2025)(x−2026)2f'(x) = (x - 2024)^3(x - 2025)(x - 2026)^2, we need to find local maxima of g(x)=f(x)g(x) = \sqrt{f(x)}.

Since g(x)=f(x)g(x) = \sqrt{f(x)}, differentiating:

g′(x)=f′(x)2f(x)g'(x) = \frac{f'(x)}{2\sqrt{f(x)}}

For critical points, g′(x)=0g'(x) = 0 when f′(x)=0f'(x) = 0, giving us x=2024,2025,2026x = 2024, 2025, 2026.


To determine which critical points are local maxima, we analyze the sign of f′(x)f'(x) in each interval.

The factor (x−2026)2(x - 2026)^2 is always non-negative, so the sign depends on (x−2024)3(x−2025)(x - 2024)^3(x - 2025):

Interval(x−2024)3(x - 2024)^3(x−2025)(x - 2025)f′(x)f'(x) signf(x)f(x) behavior
x<2024x < 2024−-−-++Increasing
2024<x<20252024 < x < 2025++−-−-Decreasing
x>2025x > 2025++++++Increasing

From the behavior of f(x)f(x):

  • At x=2024x = 2024: ff changes from increasing to decreasing → local maximum
  • At x=2025x = 2025: ff changes from decreasing to increasing → local minimum
  • At x=2026x = 2026: ff keeps increasing (no sign change) → no extremum

Since g(x)=f(x)g(x) = \sqrt{f(x)} is a monotonically increasing transformation of f(x)f(x) (for f>0f > 0), gg inherits the same extremum behavior as ff.

Therefore, g(x)g(x) has a local maximum only at x=2024x = 2024.

The answer is 1.

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