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Published on: 30/09/2019
Relations and Functions
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1.
If a function \(f:R\rightarrow R\) be defined by
\(f(x)=\begin{cases} 3x-2,\quad x<0 \\ 1,\quad \quad \quad \quad x=0 \\ 4x+1,\quad x>0 \end{cases}\)
Find f(1), f(-1), f(0), f(2).
2.
Find the domain of the function f defined by \(f(x)=\sqrt { 4-x } +\frac { 1 }{ \sqrt { { x }^{ 2 }-1 } } \)
3.
If A = {a,d}, B = {b,c,e} and C = {b,c,f}, then verify that \(A\times (B\cup C)=(A\times B)\cup (A\times C)\)
4.
If X = {1, 2, 3, 4, 5}, Y = {1, 2, 5, 6, 7, 9, 10, 11, 12, 13, 14} and \(f:X\rightarrow Y\) be defined by f(x) = 2x+3, then find the domainand range of f.
5.
If f and g be two real function defined by \(f\left( x \right) =\sqrt { x+1 } \)and \(g\left( x \right) =\sqrt { 9-{ x }^{ 2 } } \) .Then, describe each of the following functions. \(\frac { f }{ g } \)
6.
If A and B are any two non-empty sets, then prove that A x B = B x A \(\Leftrightarrow \) A = B
7.
If A \(\subset\) B then prove that A x A = (A x B) \(\cap\) (B x A).
8.
The relation f is defined by
\(f(x)=\begin{cases} { x }^{ 2 },\quad 0\le x \le 3 \\ 3x,\quad3\le x<10\end{cases}\)
The relation g is defined by
\(g(x)=\begin{cases} { x }^{ 2 },\quad 0\le x \le 2 \\ 3x,\quad2\le x\le10\end{cases}\)
Show that f is a function and g is not a function.
9.
Find the domain and range of the following real functions \(f(x)=\sqrt{9-x^2}\)
10.
Let A= {x, y} and B = {a, b}, How many relations are there from A to B. Write all the relations
11.
Determine the domain and range of the relation defined as: R = {(a, b) : a, b\(\in\)N, a < 5, b = 3a + 1}
1.
f(1) = 5
f(-1) = -5
f(0) = 1
f(2) = 9
2.
Domain = \((-\infty ,-1)\cup (1,4)\)
3.
To determine \(A\times (B\cup C)\)
\(B\cup C\) = {b,c,e} \(\cup \) {b,c,f} = {b,c,e,f}
\(\therefore \)\(A\times (B\cup C)\) = {a,d} x {b,c,e,f}
={(a,b),(a,c),(a,e),(a,f),(d,b),(d,c)(d,e),(d,f)}........(i)
To determine \((A\times B)\cup (A\times C)\)
\(A\times B\)={a,d} x {b,c,e}
={(a,b),(a,c),(a,e),(d,b),(d,c),(d,e)}
\(A\times C\)={a,d} x {b,c,f}
={(a,b),(a,c),(a,f),(d,b),(d,c),(d,f)}
\(\therefore \)\((A\times B)\cup (A\times C)\) = {(a,b),(a,c),(a,e),(a,f),(d,b),(d,c),(d,e),(d,f)}......(ii)
From Eqs.(i) and (ii) we get
\(A\times (B\cup C)=(A\times B)\cup (A\times C)\)
4.
Domain = {1, 2, 3, 4, 5} Range = {5, 7, 9, 11, 13}
5.
Domain \((f)\cap \) Domain \((g)=\left[ -1,3 \right] \)
\(\left( \frac { f }{ g } \right) (x)=\sqrt { \frac { x+1 }{ 9-{ x }^{ 2 } } } \)
6.
Let A = B.
Now A = B\(\Rightarrow\)A x B = A x A....(i)
and A = B \(\Rightarrow\) B x A = A x A...(ii)
From (i) and (ii), we have
AxB=BxA
Let A x B = B x A and x be any element of A and Y be any element of B.
\(\Rightarrow\) (x, y) \(\in\)A x B
\(\Rightarrow\) (x, y)\(\in\) B x A (\(\because\)A x B = B x A)
\(\Rightarrow\) X\(\in\)B
\(\therefore\) x\(\in\)A\(\Rightarrow\) x\(\in\)B
\(\therefore\) A\(\subset\)B ...(iii)
Let x be any element of B and y be any element of A.
\(\Rightarrow\)(x, y) \(\in\)B x A
\(\Rightarrow\) (x, y)\(\in\) A x B (\(\because\) A x B = B x A)
\(\Rightarrow\) x\(\in\)A
\(\therefore\) x\(\in\)B\(\Rightarrow\) xEA
\(\therefore\) B \(\subset\)A...(iv)
From (iii) and (iv), we have
A=B
7.
Let (x, y) \(\in\) A x A
\(\Rightarrow x,y \in A\) \((\therefore A\subset B)\)
\(\Rightarrow x,y \in B\)
\(\therefore\) \(x,y \in A,y\in B\Rightarrow (x,y)\in A\times B\)
x \(\in\) B, Y\(\in\)A \(\Rightarrow\) (x, y) \(\in\) B x A
\(\Rightarrow\) (x, y)\(\in\) (A x B) \(\cap\) (B x A)
\(\therefore\) A x A\(\subset\)(A x B) \(\cap\) (B x A) ...(i)
Let (x, y)\(\in\)(A x B) \(\cap\)(B x A)
\(\Rightarrow\) (x, y)\(\in\) A x B and (x, y) \(\in\) B x A
\(\Rightarrow\) [x\(\in\) A and x\(\in\) B] and [x\(\in\) Band Y\(\in\)A]
\(\Rightarrow\) x, Y\(\in\)A \(\Rightarrow\) x, Y\(\in\)A x A
\(\therefore\)(A x B) \(\cap\) (B x A) \(\subset\)A x A ... (ii)
From (i) and (ii), we have
\(\therefore\) A x A = (A x B)\(\cap\) (B x A).
8.
Here
f(x) = x2 0\(\le\)x \(\le\)3
f(x) = 3x 3 \(\le\) x \(\le\)10
At x=3
f(3) = (3)2 = 9 and f(3) = 3 x 3 = 9.
We observe that f(x) takes unique value at each point in its domain [0,10]. So f is a function.
Now g(x) = x2 0\(\le\)x \(\le\)2
g(x) = 3x 2\(\le\)x \(\le\)10
At x=2
g(2) = (2)2 = 4 and g(2) = 3 x 2 = 6
So g(x) does not have unique value at x = 2.
Hence g(x) is not a function.
9.
f(x) = \(\sqrt{9-x^{2}}\)
Since \(\sqrt{9-x^{2}}\) is defined for all real numbers that are greater than or equal to –3 and less than or equal to 3, the domain of f(x) is {x : –3 ≤ x ≤ 3} or [–3, 3].
For any value of x such that –3 ≤ x ≤ 3, the value of f(x) will lie between 0 and 3.
∴ The range of f(x) is {x: 0 ≤ x ≤ 3} or [0, 3].
10.
16; \(\phi\), {(x, a)}, {(x, b)}, {(y, a)}, {(y, b)}
{(x, a), (x, b)}, {(x, a), (y, a)}, {(x, a), (y, b)}, {(x, b), (y, a)}
{(x, b), (y, b)}, {(y, a), (y, b)}, {(x, a), (x, b), (y, a)}
{(x, a), (x, b), (y, b)}, {(x, a), (y, a), (y, b)}, {(x, b), (y, a), (y, b)}
{(x, a), (x, b), (y, a), (y, b)}
11.
Domain of R = {1, 2, 3, 4}
Range of R = {4, 7, 10, 13}
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