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1)

Let   f(x)=sin[π6sin(π2sinx)]  for all x ε  R and   g(x)=(π/2)sinx4 for all x ε  R . Let (fog)(x)  denotes f(g(x)) and (gof)(x) denotes g{f(x)} . Then, which of the following is /are true?


A) Range of f is [12,12]

B) Range of fog is [12,12]

C) limx0f(x)g(x)=π6

D) There is an an x e R such that (gof)(x)=1

Answer:

Option A,B,C

Explanation:

(a)       f(x)=sin[π6sinπ2(sinx)],xϵR

                      =  sin(π6sinθ),θϵ[π2,π2],

   where               θ=π2sinx

                                      = sinα,αϵ[π6,π6],

where   α=π6sinθ

        f(x)\epsilon  \left[-\frac{1}{2},\frac{1}{2}\right]

   Hence, range of      f(x)\epsilon  \left[-\frac{1}{2},\frac{1}{2}\right]

  So,  option (a) is correct.

 (b)    f\left\{g(x)\right\}=f(t),t\epsilon \left[- \frac{\pi}{2},\frac{\pi}{2}\right]

   \Rightarrow    f(t)\epsilon  \left[-\frac{1}{2},\frac{1}{2}\right]

\therefore      Option (b) is correct.

   (c)   \lim_{x \rightarrow 0}\frac{f(x)}{g(x)}

                                        =\lim_{x \rightarrow 0}\frac{\sin\left[\frac{\pi}{6}\sin(\frac{\pi}{2}\sin x)\right]}{\frac{\pi}{2}(\sin x)}

                          =\lim_{x \rightarrow 0}\frac{\sin\left[\frac{\pi}{6}\sin(\frac{\pi}{2}\sin x)\right]}{\frac{\pi}{6}\sin(\frac{\pi}{2}\sin x)}

                                                      \frac{\frac{\pi}{6}\sin(\frac{\pi}{2}\sin x)}{(\frac{\pi}{2}\sin x)}

                              =  1\times \frac{\pi}{6} \times 1=\frac{\pi}{6}

  \therefore    Option (c) is correct.

  (d) g{ f(x)}=1

\Rightarrow                  \frac{\pi}{2}\sin\left\{f(x)\right\}=1

\Rightarrow               \sin\left\{f(x)\right\}=\frac{2}{\pi}                    .........(i)

 But               f(x)\epsilon \left[-\frac{1}{2},\frac{1}{2}\right]\subset\left[ -\frac{\pi}{6},\frac{\pi}{6}\right]

\therefore   \sin \left\{  f(x)\right\}\epsilon \left[-\frac{1}{2},\frac{1}{2}\right] ..............(ii)

\Rightarrow      \sin \left\{ f(x)\right\}\neq\frac{2}{\pi}

    [from Eqs(i) and  (ii) ]

 i.e, no solution

 \therefore    Option (d) is not correct.