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JEE Advanced 2015Paper 1
Exam
JEE Advanced
Year
2015
Paper
Paper 1
Subject
Mathematics
Chapter
Functions

JEE Advanced 2015 · Paper 1 · Mathematics · Functions

Let f(x) = ((π)/(6) ((π)/(2)sin x)) , for all x ∈ R and g(x) =...

Let f(x)=sin⁡(π6sin⁡(π2sinx))f\left(x\right) = \sin \left(\dfrac{\pi}{6}\sin \left(\dfrac{\pi}{2}sin x\right)\right), for all x∈Randx \in R andg\left(x\right) = \dfrac{\pi}{2}sin x,forall, for allx \in R.Let(fog)(x). Let \left(f o g\right)\left(x\right) denote f(g(x))f\left(g\left(x\right)\right) and \left(g o f\right)(x)\left(x\right) denote g(f(x))g\left(f\left(x\right)\right). Then which of the following is (are) true?Let f(x) = ((π)/(6) ((π)/(2)sin x)) , for all x ∈ R and g(x) = (π)/(2)sin x , for all x ∈ R . Let (f o g)(x) denote

Options

  1. ARange of ff is [−12,12]\left[- \dfrac{1}{2}, \dfrac{1}{2}\right]
  2. BRange of fogf o g is [−12,12]\left[- \dfrac{1}{2}, \dfrac{1}{2}\right]
  3. Clim⁡x→0f(x)g(x)=π6\lim_{x \to 0} \dfrac{f ( x )}{g ( x )} = \dfrac{\pi}{6}
  4. DThere is an x∈Rx \in R such that \left(g o f\right)\left(x\right) = 1

Correct answer

A. Range of ff is [−12,12]\left[- \dfrac{1}{2}, \dfrac{1}{2}\right]

Step-by-step solution

f(x)=sin⁡(π6sin⁡(π2sinx))f\left(x\right) = \sin \left(\dfrac{\pi}{6}\sin \left(\dfrac{\pi}{2}sin x\right)\right)
−π2≤π2sinx≤π2\dfrac{- \pi}{2} \le \dfrac{\pi}{2}sin x \le \dfrac{\pi}{2}
−1≤sin⁡(π2sinx)≤1- 1 \le \sin \left(\dfrac{\pi}{2}sin x\right) \le 1
sin⁡(−π6)\lesin(π6(sin⁡(π2sinx)))≤sinπ6\sin \left(\dfrac{- \pi}{6}\right) \lesin \left(\dfrac{\pi}{6}\left(\sin \left(\dfrac{\pi}{2}sin x\right)\right)\right) \le sin \dfrac{\pi}{6}
−12≤sin⁡(π6(sin⁡(π2sinx)))≤12\dfrac{- 1}{2} \le \sin \left(\dfrac{\pi}{6}\left(\sin \left(\dfrac{\pi}{2}sin x\right)\right)\right) \le \dfrac{1}{2}
f(g(x))=sin⁡(π6(sin⁡(π2sin⁡(π2sinx))))f\left(g\left(x\right)\right) = \sin \left(\dfrac{\pi}{6}\left(\sin \left(\dfrac{\pi}{2}\sin \left(\dfrac{\pi}{2}sin x\right)\right)\right)\right)
−1≤sin⁡(π2sinx)≤1- 1 \le \sin \left(\dfrac{\pi}{2}sin x\right) \le 1
−π2≤π2sin⁡(π2sinx)≤π2\dfrac{- \pi}{2} \le \dfrac{\pi}{2}\sin \left(\dfrac{\pi}{2}sin x\right) \le \dfrac{\pi}{2}
−1≤sin⁡(π2(sin⁡(π2sinx)))≤1- 1 \le \sin \left(\dfrac{\pi}{2}\left(\sin \left(\dfrac{\pi}{2}sin x\right)\right)\right) \le 1
−π6≤π6sin⁡(π2(sin⁡(π2sinx)))≤π6- \dfrac{\pi}{6} \le \dfrac{\pi}{6}\sin \left(\dfrac{\pi}{2}\left(\sin \left(\dfrac{\pi}{2}sin x\right)\right)\right) \le \dfrac{\pi}{6}
−12≤sin⁡(π6sin⁡(π2sin⁡(π2sinx)))≤12\dfrac{- 1}{2} \le \sin \left(\dfrac{\pi}{6}\sin \left(\dfrac{\pi}{2}\sin \left(\dfrac{\pi}{2}sin x\right)\right)\right) \le \dfrac{1}{2}
lim⁡x→0f(x)g(x)=lim⁡x→0sin⁡(π6sin⁡(π2sin⁡x))π2sinx×π6sin⁡(π2sinx)π6sin⁡(π2sinx)\lim_{x \to 0}\dfrac{f\left(x\right)}{g\left(x\right)} = \lim_{x \to 0} \dfrac{\sin \left(\dfrac{\pi}{6}\sin \left(\dfrac{\pi}{2}\sin x\right)\right)}{\dfrac{\pi}{2}sin x} \times \dfrac{\dfrac{\pi}{6}\sin \left(\dfrac{\pi}{2}sin x\right)}{\dfrac{\pi}{6}\sin \left(\dfrac{\pi}{2}sin x\right)}

=lim⁡x→0π6sin⁡(π2sinx)π2sinx=π6= \lim_{x \to 0} \dfrac{\pi}{6}\dfrac{\sin \left(\dfrac{\pi}{2}sin x\right)}{\dfrac{\pi}{2}sin x} = \dfrac{\pi}{6}.

Let f(x) = ((π)/(6) ((π)/(2)sin x)) , for all x ∈ R and g(x) = (π)/(2)sin x , for all x ∈ R . Let (f o g)(x) denote
Range of g\left(f\left(x\right)\right)is[π2sin⁡(−12),π2sin12]is \left[\dfrac{\pi}{2}\sin \left(\dfrac{- 1}{2}\right), \dfrac{\pi}{2}sin \dfrac{1}{2}\right]
=[−π2sin12,π2sin12]= \left[- \dfrac{\pi}{2}sin \dfrac{1}{2}, \dfrac{\pi}{2}sin \dfrac{1}{2}\right]
Hence, 11, does not belong to this range.

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