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For which of the following real functions, x=0x=0 is a point of local maxima?

(A) f(x)=4x4−3x3−2x2+1f(x)=4x^4-3x^3-2x^2+1

(B) f(x)=3x5+2x4−7x2+4f(x)=3x^5+\sqrt{2}x^4-7x^2+4

(C) f(x)=5x4−3x2+ef(x)=5x^4-3x^2+e

(D) f(x)=−3x3+2x2−9f(x)=-3x^3+2x^2-9

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 1

Near x=0x=0 the derivative is dominated by its lowest-degree term.

(A) f′≈−4xf'\approx-4x, (B) f′≈−14xf'\approx-14x, (C) f′≈−6xf'\approx-6x: each changes from positive to negative at x=0x=0, giving a local maximum.

(D) f′=−9x2+4x≈4xf'=-9x^2+4x\approx4x, which changes from negative to positive, so x=0x=0 is a local minimum there.

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