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JEE Advanced 2020Paper 1
Exam
JEE Advanced
Year
2020
Paper
Paper 1
Subject
Mathematics
Chapter
Functions

JEE Advanced 2020 · Paper 1 · Mathematics · Functions

If the function f: R → R is defined by f(x) = |x|(x - x) , then...

If the function f:R→Rf: R \to R is defined by f(x)=∣x∣(x−sin⁡x)f\left(x\right) = \left|x\right|\left(x - \sin x\right), then which of the following statements is TRUE?If the function f: R → R is defined by f(x) = |x|(x - x) , then which of the following statements is TRUE?

Options

  1. Aff is one-one, but NOT onto
  2. Bff is onto, but NOT one-one
  3. Cff is BOTH one-one and onto
  4. Dff is NEITHER one-one NOR onto

Correct answer

C. ff is BOTH one-one and onto

Step-by-step solution

f(x)=f\left(x\right) =\left|x\right|\left(x - \sin x\right)isoddfunction [∵f(−x)=−f(x)]is odd function \left[∵ f \left(- x\right) = - f \left(x\right)\right]

Now, f(x)=x2−xsinx∀x≥0f\left(x\right) = {x}^{2} - xsinx \forall x \ge 0

⇒f′(x)=2x−xcosx−sin⁡x⇒ {f}^{'}\left(x\right) = 2x - xcosx - \sin x

⇒f′(x)=(x−sin⁡x)+x(1−cos⁡x)>0⇒ {f}^{'}\left(x\right) = \left(x - \sin x\right) + x \left(1 - \cos x\right) > 0

∴∴Graph of y=f(x) willbey = f \left(x\right) will be

If the function f: R → R is defined by f(x) = |x|(x - x) , then which of the following statements is TRUE?

From graph, it's one-one and onto both.

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