arthham

JEE Advanced 2018 · Relations and Functions (Class 12)

Let E1={x∈R:x≠1 and xx−1>0}E_1 = \left\{ x \in \mathbb{R} : x \neq 1 \text{ and } \frac{x}{x-1} > 0 \right\} and E2={x∈E1:sin⁡−1(log⁡e(xx−1)) is a real number}E_2 = \left\{ x \in E_1 : \sin^{-1}\left( \log_e\left( \frac{x}{x-1} \right) \right) \text{ is a real number} \right\}. (Here, the inverse trigonometric function sin⁡−1x\sin^{-1} x assumes values in [−π2,π2]\left[ -\frac{\pi}{2}, \frac{\pi}{2} \right].) Let f:E1→Rf : E_1 \to \mathbb{R} be the function defined by f(x)=log⁡e(xx−1)f(x) = \log_e\left( \frac{x}{x-1} \right) and g:E2→Rg : E_2 \to \mathbb{R} be the function defined by g(x)=sin⁡−1(log⁡e(xx−1))g(x) = \sin^{-1}\left( \log_e\left( \frac{x}{x-1} \right) \right). | List-I | List-II | | --- | --- | | P. The range of f is | 1. (−∞,11−e]∪[ee−1,∞)\left( -\infty, \frac{1}{1-e} \right] \cup \left[ \frac{e}{e-1}, \infty \right) | | Q. The range of g contains | 2. (0,1)(0, 1) | | R. The domain of f contains | 3. [−12,12]\left[ -\frac{1}{2}, \frac{1}{2} \right] | | S. The domain of g is | 4. (−∞,0)∪(0,∞)(-\infty, 0) \cup (0, \infty) | | | 5. (−∞,ee−1]\left( -\infty, \frac{e}{e-1} \right] | | | 6. (−∞,0)∪(12,ee−1](-\infty, 0) \cup \left( \frac{1}{2}, \frac{e}{e-1} \right] |

Answer: A. P→4; Q→2; R→1; S→1P \to 4;\ Q \to 2;\ R \to 1;\ S \to 1

Watch this solved on the board The full walkthrough, written out a line at a time with narration explaining each step as it appears. Pause anywhere and ask why a line is there. Free to watch

Or read the worked solution below. Jump to the steps ↓

Written solution

Let E₁ = { x ∈ R : x ≠ 1 and x/(x-1) > 0 } and E₂ = { x ∈ E₁ : sin⁻¹( logₑ( x/(x-1) ) ) is a real number }. (Here, the inverse trigonometric function sin⁻¹ x assumes values in [ -π/2, π/2 ].) Let f : E₁ → R be the function defined by f(x) = logₑ( x/(x-1) ) and g : E₂ → R be the function defined by g(x) = sin⁻¹( logₑ( /

E1={x:x≠1, xx−1>0}E_1 = \left\{ x : x \neq 1,\ \dfrac{x}{x-1} > 0 \right\}

E2={x∈E1:sin⁡−1 ⁣(ln⁡xx−1)∈R}E_2 = \left\{ x \in E_1 : \sin^{-1}\!\left( \ln\dfrac{x}{x-1} \right) \in \mathbb{R} \right\}

f(x)=ln⁡xx−1,g(x)=sin⁡−1 ⁣(ln⁡xx−1)f(x) = \ln\dfrac{x}{x-1},\qquad g(x) = \sin^{-1}\!\left( \ln\dfrac{x}{x-1} \right)

Match: P(range of f), Q(range of g), R(domain of f), S(domain of g)\text{Match: } P(\text{range of }f),\ Q(\text{range of }g),\ R(\text{domain of }f),\ S(\text{domain of }g)

xx−1>0  ⟺  x<0 or x>1\dfrac{x}{x-1} > 0 \iff x < 0 \text{ or } x > 1

E1=(−∞,0)∪(1,∞)E_1 = (-\infty, 0) \cup (1, \infty)

t=xx−1:x<0⇒t∈(0,1);x>1⇒t∈(1,∞)t = \dfrac{x}{x-1}:\quad x<0 \Rightarrow t\in(0,1);\quad x>1 \Rightarrow t\in(1,\infty)

Range(f)=(−∞,0)∪(0,∞)=R∖{0}\text{Range}(f) = (-\infty,0)\cup(0,\infty) = \mathbb{R}\setminus\{0\}

⇒ P→4\Rightarrow\ P \to 4

Domain(f)=E1=(−∞,0)∪(1,∞)\text{Domain}(f) = E_1 = (-\infty,0)\cup(1,\infty)

(−∞,11−e]∪[ee−1,∞)⊂E1\left(-\infty,\tfrac{1}{1-e}\right]\cup\left[\tfrac{e}{e-1},\infty\right) \subset E_1

⇒ R→1\Rightarrow\ R \to 1

−1≤ln⁡t≤1  ⟺  1e≤t≤e-1 \le \ln t \le 1 \iff \tfrac{1}{e} \le t \le e

x=tt−1⇒Domain(g)=(−∞,11−e]∪[ee−1,∞)x = \dfrac{t}{t-1} \Rightarrow \text{Domain}(g) = \left(-\infty,\tfrac{1}{1-e}\right]\cup\left[\tfrac{e}{e-1},\infty\right)

⇒ S→1\Rightarrow\ S \to 1

ln⁡t∈[−1,1]∖{0}⇒Range(g)=[−π2,π2]∖{0}\ln t \in [-1,1]\setminus\{0\} \Rightarrow \text{Range}(g) = \left[-\tfrac{\pi}{2},\tfrac{\pi}{2}\right]\setminus\{0\}

(0,1)⊂Range(g),[−12,12]⊄Range(g)(0,1) \subset \text{Range}(g),\qquad \left[-\tfrac12,\tfrac12\right] \not\subset \text{Range}(g)

⇒ Q→2\Rightarrow\ Q \to 2

P→4,Q→2,R→1,S→1P \to 4,\quad Q \to 2,\quad R \to 1,\quad S \to 1

option (1)\boxed{\text{option } (1)}

More from Relations and Functions (Class 12)

All 19 Relations and Functions (Class 12) questions →