Question Details

The interval on which the function f(x) = x2 e-x is increasing , is equal to

Options

A

(-∞, ∞)

B

(-∞, 2) ∪ (2, ∞)

C

(-2, 0)

D

(0, 2)

Show Answer

Correct Answer :

Option D

(0, 2)

Solution :

The correct option is (0, 2).

To find the interval on which the function f(x)=x2e-x is increasing, we need to find where its first derivative is positive, i.e., f'(x)>0.

First, let's find the derivative of f(x) with respect to x using the product rule:
f'(x) = ddx x2 · e-x + x2 · ddx e-x

Calculating the derivatives of the individual components:
f'(x) = 2xe-x + x2 -e-x

Factoring out the common terms xe-x:
f'(x) = xe-x (2-x)

For the function to be increasing, we require:
f'(x)>0
xe-x(2-x)>0

Since the exponential term e-x is always positive for all real values of x, the sign of the derivative depends entirely on the product x(2-x). Thus, we must have:
x(2-x)>0

Multiplying both sides by -1 changes the direction of the inequality:
x(x-2)<0

The product is negative when x lies strictly between the roots of the expression, which are 0 and 2. Therefore, the inequality holds when:
0<x<2

Expressing this in interval notation, the function is increasing on the interval (0, 2).

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