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The function f(x)=2log⁡e(x−2)−x2+4x+1,(x>2)f(x) = 2\log_e(x-2) - x^2 + 4x + 1, (x > 2) is increasing on the interval:

Solution

✅ Correct Option: 3

A function is increasing when its derivative is positive.

Given: f(x)=2log⁡e(x−2)−x2+4x+1f(x) = 2\log_e(x-2) - x^2 + 4x + 1

Differentiating term by term:

ddx[2log⁡e(x−2)]=2x−2\frac{d}{dx}[2\log_e(x-2)] = \frac{2}{x-2}

ddx[−x2]=−2x\frac{d}{dx}[-x^2] = -2x

ddx[4x]=4\frac{d}{dx}[4x] = 4

ddx[1]=0\frac{d}{dx}[1] = 0

Therefore:

f′(x)=2x−2−2x+4f'(x) = \frac{2}{x-2} - 2x + 4


For the function to be increasing:

f′(x)>0f'(x) > 0

2x−2−2x+4>0\frac{2}{x-2} - 2x + 4 > 0

2x−2>2x−4\frac{2}{x-2} > 2x - 4

2x−2>2(x−2)\frac{2}{x-2} > 2(x - 2)

1x−2>(x−2)\frac{1}{x-2} > (x - 2)


Since x>2x > 2, we have (x−2)>0(x-2) > 0.

Multiplying both sides by (x−2)(x-2):

1>(x−2)21 > (x-2)^2

(x−2)2<1(x-2)^2 < 1


Taking the square root:

∣x−2∣<1|x-2| < 1

−1<x−2<1-1 < x-2 < 1

1<x<31 < x < 3


The original function has domain x>2x > 2.

Combining x>2x > 2 and 1<x<31 < x < 3:

2<x<32 < x < 3

Therefore, the function is increasing on the interval (2,3)(2, 3).

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