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JEE Advanced 2016Paper 1
Exam
JEE Advanced
Year
2016
Paper
Paper 1
Subject
Mathematics
Chapter
Differentiation

JEE Advanced 2016 · Paper 1 · Mathematics · Differentiation

Let f: R → R, g: R → R and h: R → R be differentiable functions...

Let f:R→R,g:R→Rf: R \to R, g: R \to R and h:R→Rh: R \to R be differentiable functions such that f(x)=x3+3x+2,g(f(x))=xf\left(x\right) = {x}^{3} + 3x + 2, g\left(f\left(x\right)\right) = x and h(g(g(x)))=xh\left(g\left(g\left(x\right)\right)\right) = x , for all x∈R.x \in R . Then,

Options

  1. Ag′(2)=115{g}^{′}\left(2\right) = \dfrac{1}{15}
  2. Bh′(1)=666{h}^{′}\left(1\right) = 666
  3. Ch(0)=16h\left(0\right) = 16
  4. Dh(g(3))=36h\left(g\left(3\right)\right) = 36

Correct answer

B. h′(1)=666{h}^{′}\left(1\right) = 666

Step-by-step solution

If f′(x)=3x2+3{f}^{′}\left(x\right) = 3{x}^{2} + 3
⇒g(f(x))=x⇒ g\left(f\left(x\right)\right) = x
⇒g′(f(x))=1f′(x)⇒ {g}^{′}\left(f\left(x\right)\right) = \dfrac{1}{{f}^{′}\left(x\right)}
Also f\left(0\right) = 2((Put x = 0)<br/>So,)<br />So,{g}^{′}\left(2\right) = \dfrac{1}{{f}^{′}\left(0\right)}<br/><br />⇒ g′\left(2\right) = \dfrac{1}{3}<br/>If<br />Ifh ( g\left(g\left(x\right)\right) = x<br/><br />{h}^{′}\left(g\left(g\left(x\right)\right)\right) = \dfrac{1}{{g}^{′}\left(g\left(x\right)\right).{g}^{′}\left(x\right)}<br/>If,<br />If,g\left(g\left(x\right)\right) = 1 g ( f\left(x\right) ) = x ⇒ {g}^{- 1}\left(x\right) = f ( x )<br/><br />⇒ g\left(x\right) = {g}^{- 1}\left(1\right) ⇒ g\left(x\right) = f\left(1\right) = 6<br/>Tofind,<br />To find,{g}^{'}\left(6\right)useusex = 1in<br/>in<br />{g}^{'}\left(f\left(x\right)\right) = \dfrac{1}{{f}^{'}\left(1\right)}asasf \left(1\right) = 6</p><p>Tofind,</p><p>To find,{g}^{'}\left(236\right),use, usex = 6as<br/>as<br />f\left(6\right) = 236<br/><br />∴ {h}^{'}\left(1\right) = \dfrac{1}{{g}^{'}\left(6\right).{g}^{'} ( 236 )} = \dfrac{1}{\dfrac{1}{6}.\dfrac{1}{111}} ⇒ {h}^{'}\left(1\right) = 666<br/>If<br />Ifg\left(g\left(x\right)\right) = 0<br/><br />∴ g\left(x\right) = {g}^{- 1}\left(0\right) ⇒ g\left(x\right) = f\left(0\right)</p><p></p><p>⇒ g\left(x\right) = 2 ⇒ x = {g}^{- 1}\left(2\right)</p><p></p><p>⇒ x = f\left(2\right) ⇒ x = 16<br/><br />∴ h\left(0\right) = 16<br/><br />g\left(x\right) = 3 ⇒ x = {g}^{- 1}\left(3\right)</p><p></p><p>⇒ x = f\left(3\right) ⇒ x = 38<br/>So<br />Soh\left(g\left(3\right)\right) = 38$

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