Functions
Given below are two statements :
Statement I : The function $f: \mathbb{R} \to \mathbb{R}$ defined by $f(x) = \frac{x}{1 + |x|}$ is one-one.
Statement II : The function $f: \mathbb{R} \to \mathbb{R}$ defined by $f(x) = \frac{x^2 + 4x - 30}{x^2 - 8x + 18}$ is many-one.
In the light of the above statements, choose the correct answer from the options given below :
Statement I is true but Statement II is false
Both Statement I and Statement II are false
Both Statement I and Statement II are true
Statement I is false but Statement II is true
The sum of all the elements in the range of $f(x) = \text{Sgn}(\sin x) + \text{Sgn}(\cos x) + \text{Sgn}(\tan x) + \text{Sgn}(\cot x)$, $x \neq \frac{n\pi}{2}, n \in \mathbb{Z}$, where
$\text{Sgn}(t) = \begin{cases} 1, & \text{if } t > 0 \\ -1, & \text{if } t < 0 \end{cases}$
is :
4
0
2
-2
$\frac{7}{2}$
$-\frac{25}{6}$
$\frac{25}{6}$
$-\frac{7}{2}$
Let $f$ be a function such that $3 f(x)+2 f\left(\frac{m}{19 x}\right)=5 x, x \neq 0$, where $m=\sum\limits_{i=1}^9(i)^2$. Then $f(5)-f(2)$ is equal to
36
9
-9
18
Let $f(x)=[x]^2-[x+3]-3, x \in \mathbf{R}$, where [.] is the greatest integer funtion. Then
$f(x)=0$ for finitely many values of $x$
$f(x)<0$ only for $x \in[-1,3)$
$\int\limits_0^2 f(x) \mathrm{d} x=-6$
$f(x)>0$ only for $x \in[4, \infty)$
Let the domain of the function $f(x)=\log _3 \log _5\left(7-\log _2\left(x^2-10 x+85\right)\right)+\sin ^{-1}\left(\left|\frac{3 x-7}{17-x}\right|\right)$ be $(\alpha, \beta]$. Then $\alpha+\beta$ is equal to :
12
8
10
9
Let $f$ and $g$ be functions satisfying $f(x+y)=f(x) f(y), f(1)=7$ and $g(x+y)=g(x y), g(1)=1$, for all $x, y \in \mathbf{N}$. If $\sum\limits_{x=1}^{\mathrm{n}}\left(\frac{f(x)}{\mathrm{g}(x)}\right)=19607$, then n is equal to :
6
7
4
5
If the domain of the function $f(x)=\sin ^{-1}\left(\frac{5-x}{3+2 x}\right)+\frac{1}{\log _e(10-x)}$ is $(-\infty, \alpha] \cup[\beta, \gamma)-\{\delta\}$, then $6(\alpha+\beta+\gamma+\delta)$ is equal to
66
68
70
67
Let $f$ be a polynomial function such that $\log _2(f(x))=\left(\log _2\left(2+\frac{2}{3}+\frac{2}{9}+\ldots \ldots \infty\right)\right) \cdot \log _3\left(1+\frac{f(x)}{f(1 / x)}\right), x>0$ and $f(6)=37$. Then $\sum\limits_{\mathrm{n}=1}^{10} f(\mathrm{n})$ is equal to $\_\_\_\_$ .
Explanation:
Statement of Work :
1. $\boldsymbol{f}(\boldsymbol{x})$ is a polynomial function
2. A logarithmic equation involving function $\left.f: \log _2[f(x)]=\left[\log _2\left(2+\frac{2}{3}+\frac{2}{9}+\ldots . . \infty\right)\right] \cdot \log _3\left\{1+\frac{\boldsymbol{f}(\boldsymbol{x})}{f\left(\frac{1}{\boldsymbol{x}}\right)}\right\}\right] ; x>0$ and $\boldsymbol{f}(6)=37$
3. To evaluate the sum : $\sum\limits_{n=1}^{10} \boldsymbol{f}(n)$
$\begin{aligned} \log _2[\boldsymbol{f}(\boldsymbol{x})] & =\left[\log _2\left(2+\frac{2}{3}+\frac{2}{9}+\ldots . \infty\right)\right] \cdot\left[\log _3\left\{1+\frac{\boldsymbol{f}(\boldsymbol{x})}{\boldsymbol{f}\left(\frac{1}{\boldsymbol{x}}\right)}\right\}\right] \\ & \left.=\left[\log _2 2\left\{1+\frac{1}{3}+\left(\frac{1}{3}\right)^2+\ldots . . \infty\right\}\right] \cdot \left\lvert\, \log _3\left\{1+\frac{\boldsymbol{f}(\boldsymbol{x})}{\boldsymbol{f}\left(\frac{1}{\boldsymbol{x}}\right)}\right\}\right.\right] . \\ & =\left[\log _2 2\left(\frac{1}{1-\frac{1}{3}}\right)\right] \cdot\left[\log _3\left\{1+\frac{\boldsymbol{f}(\boldsymbol{x})}{\boldsymbol{f}\left(\frac{1}{\boldsymbol{x}}\right)}\right\}\right] \\ & \left.=\left[\log _2 3\right] \cdot \left\lvert\, \log _3\left\{1+\frac{\boldsymbol{f}(\boldsymbol{x})}{\boldsymbol{f}\left(\frac{1}{\boldsymbol{x}}\right)}\right\}\right.\right]\end{aligned}$
$\frac{\log _2[f(x)]}{\log _2 3}=\left[\log _3\left\{1+\frac{f(x)}{f\left(\frac{1}{x}\right)}\right)\right]$
$\Rightarrow \log _3[f(x)]=\log _3\left\{1+\frac{\boldsymbol{f}(\boldsymbol{x})}{f\left(\frac{1}{\boldsymbol{x}}\right)}\right\}$
$\Rightarrow f(x)=1+\frac{f(x)}{f\left(\frac{1}{x}\right)}$
$\Rightarrow $ $f(x) \cdot f\left(\frac{1}{x}\right)=f(x)+f\left(\frac{1}{x}\right)$ .....(i)
The function $\boldsymbol{f}(\boldsymbol{x})$ is a polynomial function stated in SOW where $\boldsymbol{f}(6)=37=(6)^2+1 \ldots . .(\boldsymbol{i i})$
Equation (ii) on logical analysis reduces the polynomial $\boldsymbol{f}(\boldsymbol{x})$ to the possible form below :
$f(x)=x^2+1 \ldots \ldots(i i i) \leftarrow$ Cubic powers of $x$ is not possible where $f(6)>216$
Now let us analyze the polynomial function $\boldsymbol{f}(\boldsymbol{x})$ from preconditions set in SOW :
$f(x) \cdot f\left(\frac{1}{x}\right)=\left(1+x^2\right) \cdot\left(1+\frac{1}{x^2}\right)=1+\frac{1}{x^2}+x^2+1=\left(1+x^2\right)+\left(1+\frac{1}{x^2}\right)=f(x)+f\left(\frac{1}{x}\right) \ldots . (iv)$
Equation $(i i),(i i i)$ and $(i v)$ mathematically certify the polynomial $f(x)=1+x^2$ :
$f(x)=1+x^2$
$\Rightarrow s_{10}=\sum\limits_{n=1}^{10} f(\boldsymbol{n})=\sum\limits_{\boldsymbol{n}=1}^{10}\left(1+\boldsymbol{n}^2\right)=\sum\limits_{\boldsymbol{n}=1}^{10}(1)+\sum\limits_{n=1}^{10}\left(n^2\right)$
$=10+\frac{(10) \cdot(10+1) \cdot\{(2) \cdot(10)+1\}}{6}=10+385=395$
Let $\mathrm{A}=\{1,2,3,4,5,6\}$. The number of one-one functions $f: \mathrm{A} \rightarrow \mathrm{A}$ such that $f(1) \geq 3, f(3) \leq 4$ and $f(2)+f(3)=5$, is $\_\_\_\_$ .
Explanation:
We need the number of one-one functions $f : A \to A$, where
$ A=\{1,2,3,4,5,6\} $
and the conditions are:
$f(1)\geq 3$
$f(3)\leq 4$
$f(2)+f(3)=5$
Since $f$ is one-one and domain and codomain are the same finite set, such a function is a permutation of $A$.
Now let us count carefully.
From
$ f(2)+f(3)=5 $
and since values are from $A=\{1,2,3,4,5,6\}$, the possible pairs are:
$ (f(2),f(3))=(1,4),(2,3),(3,2),(4,1) $
Also $f(3)\leq 4$, which is already satisfied by all these cases.
Now we use the condition that $f$ is one-one, so all function values must be distinct.
We also have:
$ f(1)\geq 3 \implies f(1)\in \{3,4,5,6\} $
But $f(1)$ must be different from both $f(2)$ and $f(3)$.
Case 1: $(f(2),f(3))=(1,4)$
Then $f(1)\in \{3,4,5,6\}$, but it cannot be $4$ because function is one-one.
So,
$ f(1)\in \{3,5,6\} $
Number of choices for $f(1)$ = $3$.
After fixing $f(1), f(2), f(3)$, the remaining $3$ elements of the domain can be mapped to the remaining $3$ elements of the codomain in
$ 3! = 6 $
ways.
So total in this case:
$ 3\times 6 = 18 $
Case 2: $(f(2),f(3))=(2,3)$
Then $f(1)\in \{3,4,5,6\}$, but it cannot be $3$.
So,
$ f(1)\in \{4,5,6\} $
Number of choices for $f(1)$ = $3$.
Remaining mappings can be done in
$ 3!=6 $
ways.
Total in this case:
$ 3\times 6=18 $
Case 3: $(f(2),f(3))=(3,2)$
Then $f(1)\in \{3,4,5,6\}$, but it cannot be $3$.
So again number of choices for $f(1)$ = $3$.
Remaining mappings:
$ 3!=6 $
Total:
$ 3\times 6=18 $
Case 4: $(f(2),f(3))=(4,1)$
Then $f(1)\in \{3,4,5,6\}$, but it cannot be $4$.
So number of choices for $f(1)$ = $3$.
Remaining mappings:
$ 3!=6 $
Total:
$ 3\times 6=18 $
Total number of functions
$ 18+18+18+18=72 $
Hence, the required number of one-one functions is
$ \boxed{72} $
If the domain of the function
$f(x) = \sqrt{\log_{(0.6)} (\left| \frac{2x-5}{x^2-4} \right|)}$ is $(-\infty, a] \cup \{b\} \cup [c, d) \cup (e, \infty)$, then the value of $a + b + c + d + e$ is ________.
Explanation:
For domain $\log _{0.6}\left|\frac{2 x-5}{x^2-4}\right| \geq 0$
$\left|\frac{2x-5}{x^2-4}\right| \leq 1 \quad \& \quad x \neq \frac{5}{2} \qquad \ldots..\,(1)$
$-1 \leq \frac{2x-5}{x^2-4} \leq 1$
$\frac{2x-5}{x^2-4} + 1 \geq 0$
$\frac{x^2+2x-9}{x^2-4} \geq 0$
$\frac{(x+1)^2-10}{(x-2)(x+2)} \geq 0$
$x \in \left(-\infty, -1-\sqrt{10}\right] \cup (-2,2) \cup \left[-1+\sqrt{10}, \infty\right) \qquad \ldots..(2)$
$\frac{2x-5}{x^2-4} - 1 \leq 0$
$\frac{2x-5-x^2+4}{x^2-4} \leq 0$
$\frac{x^2-2x+1}{x^2-4} \geq 0$
$\frac{(x-1)^2}{(x-2)(x+2)} \geq 0$
$x \in (-\infty,-2) \cup (2,\infty) \cup \{1\} \qquad \ldots..(3)$
$(1) \cap (2) \cap (3)$
$x \in \left(-\infty,-1-\sqrt{10}\right] \cup \{1\} \cup \left[-1+\sqrt{10}, \frac{5}{2}\right) \cup \left(\frac{5}{2}, \infty\right)$
$a+b+c+d+e=-2+1+5=4$
Let $f: \mathbf{R} \rightarrow \mathbf{R}$ be defined as $f(x)=\frac{2 x^2-3 x+2}{3 x^2+x+3}$. Then $f$ is :
both one-one and onto
one-one but not onto
onto but not one-one
neither one-one nor onto
Let [ • ] denote the greatest integer function. If the domain of the function $f(x)=\sin ^{-1}\left(\frac{x+[x]}{3}\right)$ is $[\alpha, \beta)$, then $\alpha^2+\beta^2$ is equal to:
2
5
10
13
For the function $f:[1, \infty) \rightarrow[1, \infty)$ defined by $f(x)=(x-1)^4+1$, among the two statements:
(I) The set $\mathrm{S}=\left\{x \in[1, \infty): f(x)=f^{-1}(x)\right\}$ contains exactly two elements, and
(II) The set $\mathrm{S}=\left\{x \in[1, \infty): f(x)=f^{-1}(x+1)\right\}$ is an empty set,
only (I) is TRUE
only (II) is TRUE
both (I) and (II) are TRUE
neither (I) nor (II) is TRUE
Let for some $\alpha \in \mathbb{R}, f: \mathbb{R} \rightarrow \mathbb{R}$ be a function satisfying $f(x+y)=f(x)+2 y^2+y+\alpha x y$ for all $x, y \in \mathbb{R}$. If $f(0)=-1$ and $f(1)=2$, then the value of $\sum\limits_{n=1}^5(\alpha+f(n))$ is :
110
140
150
170
Let [•] denote the greatest integer function. If the domain of the function
$f(x)=\cos ^{-1}\left(\frac{4 x+2[x]}{3}\right)$ is $[\alpha, \beta]$, then $12(\alpha+\beta)$ is equal to :
6
8
9
4
The number of functions $f:\{1,2,3,4\} \rightarrow\{a, b, c\}$, which are not onto, is :
48
45
51
35
If the range of the function $ f(x) = \frac{5-x}{x^2 - 3x + 2} , \ x \neq 1, 2, $ is $ (-\infty , \alpha] \cup [\beta, \infty) $, then $ \alpha^2 + \beta^2 $ is equal to :
188
192
190
194
Let the domains of the functions $f(x)=\log _4 \log _3 \log _7\left(8-\log _2\left(x^2+4 x+5\right)\right)$ and $\mathrm{g}(x)=\sin ^{-1}\left(\frac{7 x+10}{x-2}\right)$ be $(\alpha, \beta)$ and $[\gamma, \delta]$, respectively. Then $\alpha^2+\beta^2+\gamma^2+\delta^2$ is equal to :
Let $f, g:(1, \infty) \rightarrow \mathbb{R}$ be defined as $f(x)=\frac{2 x+3}{5 x+2}$ and $g(x)=\frac{2-3 x}{1-x}$. If the range of the function fog: $[2,4] \rightarrow \mathbb{R}$ is $[\alpha, \beta]$, then $\frac{1}{\beta-\alpha}$ is equal to
If the domain of the function $f(x)=\log _7\left(1-\log _4\left(x^2-9 x+18\right)\right)$ is $(\alpha, \beta) \cup(\gamma, o)$, then $\alpha+\beta+\gamma+\hat{o}$ is equal to
If the domain of the function $ \log_5(18x - x^2 - 77) $ is $ (\alpha, \beta) $ and the domain of the function $ \log_{(x-1)} \left( \frac{2x^2 + 3x - 2}{x^2 - 3x - 4} \right) $ is $(\gamma, \delta)$, then $ \alpha^2 + \beta^2 + \gamma^2 $ is equal to:
186
179
195
174
29
31
30
36
If $f(x)=\frac{2^x}{2^x+\sqrt{2}}, \mathrm{x} \in \mathbb{R}$, then $\sum_\limits{\mathrm{k}=1}^{81} f\left(\frac{\mathrm{k}}{82}\right)$ is equal to
Let $f: \mathbb{R} \rightarrow \mathbb{R}$ be a function defined by $f(x)=(2+3 a) x^2+\left(\frac{a+2}{a-1}\right) x+b, a \neq 1$. If $f(x+y)=f(x)+f(\mathrm{y})+1-\frac{2}{7} x \mathrm{y}$, then the value of $28 \sum\limits_{i=1}^5|f(i)|$ is
The function $f:(-\infty, \infty) \rightarrow(-\infty, 1)$, defined by $f(x)=\frac{2^x-2^{-x}}{2^x+2^{-x}}$ is :
Let $f(x)=\frac{2^{x+2}+16}{2^{2 x+1}+2^{x+4}+32}$. Then the value of $8\left(f\left(\frac{1}{15}\right)+f\left(\frac{2}{15}\right)+\ldots+f\left(\frac{59}{15}\right)\right)$ is equal to
Let $f(x)=\log _{\mathrm{e}} x$ and $g(x)=\frac{x^4-2 x^3+3 x^2-2 x+2}{2 x^2-2 x+1}$. Then the domain of $f \circ g$ is
Let $\mathrm{A}=\{1,2,3,4\}$ and $\mathrm{B}=\{1,4,9,16\}$. Then the number of many-one functions $f: \mathrm{A} \rightarrow \mathrm{B}$ such that $1 \in f(\mathrm{~A})$ is equal to :
Let the domain of the function $f(x)=\cos ^{-1}\left(\frac{4 x+5}{3 x-7}\right)$ be $[\alpha, \beta]$ and the domain of $g(x)=\log _2\left(2-6 \log _{27}(2 x+5)\right)$ be $(\gamma, \delta)$.
Then $|7(\alpha+\beta)+4(\gamma+\delta)|$ is equal to ______________.
Explanation:
$\begin{aligned} & f(x)=\cos ^{-1}\left(\frac{4 x+5}{3 x-7}\right) \\ & \Rightarrow-1 \leq\left(\frac{4 x+5}{3 x-7}\right) \leq 1 \\ & \left(\frac{4 x+5}{3 x-7}\right) \geq-1 \\ & \frac{4 x+5+3 x-7}{3 x-7} \geq 0 \\ & \Rightarrow \frac{7 x-2}{3 x-7} \geq 0 \end{aligned}$

$\begin{aligned} & x \in\left(-\infty, \frac{2}{7}\right] \cup\left(\frac{7}{3}, \infty\right) \\ & \& \frac{4 x+5}{3 x-7} \leq 1 \Rightarrow \frac{x+12}{3 x-7} \leq 0 \end{aligned}$

$\therefore$ Domain of $\mathrm{f}(\mathrm{x})$ is
$\left[-12, \frac{2}{7}\right] \alpha=-12, \beta=\frac{2}{7}$
$g(x)=\log _2\left(2-6 \log _{27}(2 x+5)\right)$
Domain
$2-6 \log _{27}(2 x+5)>0$
$\begin{array}{ll} \Rightarrow & 6 \log _{27}(2 \mathrm{x}+5)<2 \\ \Rightarrow & \log _{27}(2 \mathrm{x}+5)<\frac{1}{3} \\ \Rightarrow & 2 \mathrm{x}+5<3 \\ \Rightarrow & \mathrm{x}<-1 \end{array}$
$\& 2 x+5>0 \Rightarrow x>-\frac{5}{2}$
Domain is $\mathrm{x} \in\left(-\frac{5}{2},-1\right)$
$\begin{aligned} &\gamma=-\frac{5}{2}, \delta=-1\\ &\begin{aligned} & |7(\alpha+\beta)+4(\gamma+\delta)|=\left\lvert\, 7\left(\left.-12+\frac{2}{7}+4\left(-\frac{5}{2}-1\right) \right\rvert\,\right.\right. \\ & |-82-14|=96 \end{aligned} \end{aligned}$
Let the range of the function $f(x)=\frac{1}{2+\sin 3 x+\cos 3 x}, x \in \mathbb{R}$ be $[a, b]$. If $\alpha$ and $\beta$ ar respectively the A.M. and the G.M. of $a$ and $b$, then $\frac{\alpha}{\beta}$ is equal to
If the domain of the function $f(x)=\sin ^{-1}\left(\frac{x-1}{2 x+3}\right)$ is $\mathbf{R}-(\alpha, \beta)$, then $12 \alpha \beta$ is equal to :
Let $f(x)=\left\{\begin{array}{ccc}-\mathrm{a} & \text { if } & -\mathrm{a} \leq x \leq 0 \\ x+\mathrm{a} & \text { if } & 0< x \leq \mathrm{a}\end{array}\right.$ where $\mathrm{a}> 0$ and $\mathrm{g}(x)=(f(|x|)-|f(x)|) / 2$. Then the function $g:[-a, a] \rightarrow[-a, a]$ is
If the function $f(x)=\left(\frac{1}{x}\right)^{2 x} ; x>0$ attains the maximum value at $x=\frac{1}{\mathrm{e}}$ then :
Let $f(x)=\frac{1}{7-\sin 5 x}$ be a function defined on $\mathbf{R}$. Then the range of the function $f(x)$ is equal to :
The function $f(x)=\frac{x^2+2 x-15}{x^2-4 x+9}, x \in \mathbb{R}$ is
Let $f, g: \mathbf{R} \rightarrow \mathbf{R}$ be defined as :
$f(x)=|x-1| \text { and } g(x)= \begin{cases}\mathrm{e}^x, & x \geq 0 \\ x+1, & x \leq 0 .\end{cases}$
Then the function $f(g(x))$ is
Let $A=\{1,3,7,9,11\}$ and $B=\{2,4,5,7,8,10,12\}$. Then the total number of one-one maps $f: A \rightarrow B$, such that $f(1)+f(3)=14$, is :
$f(x)=\frac{\sqrt{x^2-25}}{\left(4-x^2\right)}+\log _{10}\left(x^2+2 x-15\right)$ is $(-\infty, \alpha) \cup[\beta, \infty)$, then $\alpha^2+\beta^3$ is equal to :
$f(x)=\left\{\begin{array}{ll}\log _{\mathrm{e}} x, & x>0 \\ \mathrm{e}^{-x}, & x \leq 0\end{array}\right.$ and
$g(x)=\left\{\begin{array}{ll}x, & x \geqslant 0 \\ \mathrm{e}^x, & x<0\end{array}\right.$. Then, gof : $\mathbf{R} \rightarrow \mathbf{R}$ is :
If $f(x)=\frac{4 x+3}{6 x-4}, x \neq \frac{2}{3}$ and $(f \circ f)(x)=g(x)$, where $g: \mathbb{R}-\left\{\frac{2}{3}\right\} \rightarrow \mathbb{R}-\left\{\frac{2}{3}\right\}$, then $(g ogog)(4)$ is equal to
If the domain of the function $f(x)=\log _e\left(\frac{2 x+3}{4 x^2+x-3}\right)+\cos ^{-1}\left(\frac{2 x-1}{x+2}\right)$ is $(\alpha, \beta]$, then the value of $5 \beta-4 \alpha$ is equal to
If the domain of the function $f(x)=\cos ^{-1}\left(\frac{2-|x|}{4}\right)+\left\{\log _e(3-x)\right\}^{-1}$ is $[-\alpha, \beta)-\{\gamma\}$, then $\alpha+\beta+\gamma$ is equal to :
If $f(x)=\left\{\begin{array}{cc}2+2 x, & -1 \leq x < 0 \\ 1-\frac{x}{3}, & 0 \leq x \leq 3\end{array} ; g(x)=\left\{\begin{array}{cc}-x, & -3 \leq x \leq 0 \\ x, & 0 < x \leq 1\end{array}\right.\right.$, then range of $(f o g)(x)$ is
Let $f: \mathbf{R}-\left\{\frac{-1}{2}\right\} \rightarrow \mathbf{R}$ and $g: \mathbf{R}-\left\{\frac{-5}{2}\right\} \rightarrow \mathbf{R}$ be defined as $f(x)=\frac{2 x+3}{2 x+1}$ and $g(x)=\frac{|x|+1}{2 x+5}$. Then, the domain of the function fog is :
Let $A=\{(x, y): 2 x+3 y=23, x, y \in \mathbb{N}\}$ and $B=\{x:(x, y) \in A\}$. Then the number of one-one functions from $A$ to $B$ is equal to _________.
Explanation:
$\begin{aligned} & A=\{(x, y) ; 2 x+3 y=23, x, y \in N\} \\ & A=\{(1,7),(4,5),(7,3),(10,1)\} \\ & B=\{x:(x, y) \in A\} \\ & B=\{1,4,7,10\} \end{aligned}$
So, total number of one-one functions from A to B is $4!=24$










