(i) ${a}$ → 1 element
(ii) ${{a}}$ → 1 element
(iii) ${a, {a}}$ → 2 elements
(iv) ${a, {a}, {{a}}}$ → 3 elements
1
Suppose that $A_i = {1, 2, 3, \ldots, i}$ for $i = 1, 2, 3, \ldots$
Then find $\displaystyle \bigcup_{i=1}^{\infty} A_i = ?$
Here $Z$ denotes the set of integers.
$,\text{Find } \displaystyle \bigcup_{i=1}^{\infty} A_i \text{ and } \bigcap_{i=1}^{\infty} A_i,\ \text{for every positive integer } i \text{ where } A_i={-i,i}.$
(Here $\mathbb Z$ denotes the set of integers.)
$A_1={-1,1},\ A_2={-2,2},\ldots$ so
$\displaystyle \bigcup_{i=1}^{\infty}A_i={\ldots,-3,-2,-1,1,2,3,\ldots}=\mathbb Z\setminus{0}$,
$\displaystyle \bigcap_{i=1}^{\infty}A_i=\varnothing$.
1
Which of the following relations are functions?
(i) ${(1,(a,b)),\ (2,(b,c)),\ (3,(c,a)),\ (4,(a,b))}$
(ii) ${(1,(a,b)),\ (2,(b,a)),\ (3,(c,a)),\ (1,(a,c))}$
(iii) ${(1,(a,b)),\ (2,(a,b)),\ (3,(a,b))}$
(iv) ${(1,(a,b)),\ (2,(b,c)),\ (1,(c,a))}$
A relation $R$ is a function iff every first component occurs exactly once.
(i) first components $1,2,3,4$ appear once each $\Rightarrow$ function.
(ii) $1$ appears twice $\Rightarrow$ not a function.
(iii) $1,2,3$ appear once each $\Rightarrow$ function.
(iv) $1$ appears twice $\Rightarrow$ not a function.
3
There is a direct flight from Trichy to New Delhi and 2 direct trains.
There are 6 trains from Trichy to Chennai and 4 trains from Chennai to Delhi.
Also, there are 2 trains from Trichy to Mumbai and 8 flights from Mumbai to New Delhi.
In how many ways can a person travel from Trichy to New Delhi?
$Q\to R = T\to F = F$, so $P\to(Q\to R)=T\to F=F$.
$P\to Q = T\to T = T$, $P\to R = T\to F = F$, hence $(P\to Q)\to(P\to R)=T\to F=F$.
Therefore $(F)\to(F)=T$.
Also $Q\vee R = T\vee F = T$, so $P\to(Q\vee R)=T\to T=T$.
2
$(A\cap B')\ \cup\ (A'\cap B)\ \cup\ (A'\cap B')$ is equal to
The floor function $f(x) = [x]$ maps every real number to the greatest integer less than or equal to $x$.
Different real numbers can have the same floor value, so it is not one-to-one,
but for every integer $n \in \mathbb{Z}$, there exists an $x \in \mathbb{R}$ such that $[x]=n$.
Hence, it is onto but not one-to-one.
4
The domain of the real-valued function
$f(x) = \sqrt{x - 3} + \sqrt{x - 4}$
is the set of all values of $x$ satisfying
For $f(x)$ to be real, both radicals must be defined:
$x - 3 \ge 0 \quad \text{and} \quad x - 4 \ge 0$
$\Rightarrow x \ge 4$
So the domain is $[4, \infty)$.