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Match List-I with List-II

List-IList-II
Function f(x)Interval for increasing/decreasing of function f(x)
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(A) f(x)=x∣x∣f(x) = x\vert x\vert (I) Decreases on (0,∞)(0, \infty)
(B) f(x)=x2+2x−5f(x) = x^2 + 2x - 5(II) Increases on (3,∞)(3, \infty)
(C) f(x)=x2−6x+9f(x) = x^2 - 6x + 9(III) Decreases on (−∞,−1)(-\infty, -1)
(D) f(x)=−x2f(x) = -x^2(IV) Increases on (−∞,∞)(-\infty, \infty)

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 2

If f′(x)>0f'(x) > 0 on an interval, the function is increasing there. If f′(x)<0f'(x) < 0, it is decreasing.


f(x)=x∣x∣f(x) = x|x|

f(x)={x2,if x≥0−x2,if x<0f(x) = \begin{cases} x^2, & \text{if } x \geq 0 \\ -x^2, & \text{if } x < 0 \end{cases}

f′(x)={2x≥0,when x≥0−2x>0,when x<0f'(x) = \begin{cases} 2x \geq 0, & \text{when } x \geq 0 \\ -2x > 0, & \text{when } x < 0 \end{cases}

f′(x)≥0f'(x) \geq 0 everywhere, so f(x)f(x) is increasing on (−∞,∞)(-\infty, \infty)

⇒\Rightarrow (A) → (IV)


f(x)=x2+2x−5f(x) = x^2 + 2x - 5

f′(x)=2x+2=2(x+1)f'(x) = 2x + 2 = 2(x + 1)

For x<−1x < -1, f′(x)<0f'(x) < 0, so f(x)f(x) is decreasing on (−∞,−1)(-\infty, -1)

⇒\Rightarrow (B) → (III)


f(x)=x2−6x+9=(x−3)2f(x) = x^2 - 6x + 9 = (x - 3)^2

f′(x)=2x−6=2(x−3)f'(x) = 2x - 6 = 2(x - 3)

For x>3x > 3, f′(x)>0f'(x) > 0, so f(x)f(x) is increasing on (3,∞)(3, \infty)

⇒\Rightarrow (C) → (II)


f(x)=−x2f(x) = -x^2

f′(x)=−2xf'(x) = -2x

For x>0x > 0, f′(x)<0f'(x) < 0, so f(x)f(x) is decreasing on (0,∞)(0, \infty)

⇒\Rightarrow (D) → (I)


(A) → (IV), (B) → (III), (C) → (II), (D) → (I)

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