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The interval in which the function g(x)=x2e−xg(x) = x^2 e^{-x} is increasing is:

Solution

✅ Correct Option: 4

Given g(x)=x2e−xg(x) = x^2 e^{-x}

To find where the function is increasing, find where g′(x)>0g'(x) > 0.

Using the product rule with f=x2f = x^2 and h=e−xh = e^{-x}:

g′(x)=(2x)(e−x)+(x2)(−e−x)g'(x) = (2x)(e^{-x}) + (x^2)(-e^{-x})

g′(x)=2xe−x−x2e−xg'(x) = 2xe^{-x} - x^2e^{-x}


Factor out the common term e−xe^{-x}:

g′(x)=e−x(2x−x2)g'(x) = e^{-x}(2x - x^2)

g′(x)=e−x⋅x(2−x)g'(x) = e^{-x} \cdot x(2 - x)


For the function to be increasing, g′(x)>0g'(x) > 0:

e−x⋅x(2−x)>0e^{-x} \cdot x(2 - x) > 0

Since e−x>0e^{-x} > 0 for all xx, the inequality reduces to:

x(2−x)>0x(2 - x) > 0


The critical points occur when x(2−x)=0x(2 - x) = 0:

x=0x = 0 or x=2x = 2

Testing the intervals:

For x<0x < 0 (test x=−1x = -1): (−1)(2−(−1))=(−1)(3)=−3<0(-1)(2 - (-1)) = (-1)(3) = -3 < 0

For 0<x<20 < x < 2 (test x=1x = 1): (1)(2−1)=(1)(1)=1>0(1)(2 - 1) = (1)(1) = 1 > 0

For x>2x > 2 (test x=3x = 3): (3)(2−3)=(3)(−1)=−3<0(3)(2 - 3) = (3)(-1) = -3 < 0


The function g(x)=x2e−xg(x) = x^2 e^{-x} is increasing on the interval (0,2)(0, 2).

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