Question
Given a non-empty set $X,$ let $*: P(X) \times P(X) \rightarrow P(X)$ be defined as $\text{A}*\text{B} =(\text{A – B})\cup(\text{B – A}),\forall\text{A},\text{B}\in\text{P(X)}.$Show that the empty set $\phi$ is the identity for the operation $*$ and all the elements $A$ of $P(X)$ are invertible with $A^{–1} = A. (\text{Hint: }(\text{A}-\phi)\cup(\phi-\text{A})=\text{A}\ \text{and }(\text{A}-\text{A})\cup(\text{A}-\text{A})=\text{A}*\text{A}=\phi).$

Answer

It is given that $*: P(X) \times P(X) \rightarrow P(X)$ is defined as $\text{A}*\text{B} =(\text{A – B})\cup(\text{B – A}),\forall\text{A},\text{B}\in\text{P(X)}.$
 Let $\text{A}\in\text{P(X)}.$
Then, we have: $\text{A}*\phi=(\text{A}-\phi)\cup(\phi-\text{A})=\text{A}\cup\phi=\text{A}$
$\phi*\text{A}=(\phi-\text{A})\cup(\text{A}-\phi)=\phi\cup\text{A}=\text{A}$
$\therefore\text{A}*\phi=\text{A}=\phi*\text{A}.\forall\text{A}\in\text{P(X)}$ Thus,
$\phi$ is the identity element for the given operation $*$.
Now, an element $\text{A}\in\text{P(X)}$ will be invertible if there exists $\text{B}\in\text{P(X)}$ such that $\text{A}*\text{B}=\phi=\text{B}*\text{A}.\ (\text{As }\phi\text{ is the identity element})$
Now, we observed that $\text{A}*\text{A}=(\text{A}-\text{A})\cup(\text{A}-\text{A})=\phi\cup\phi=\phi\ \forall\text{A}\in\text{P(X)}$
Hence, all the elements $A$ of $P(X)$ are invertible with $A^{-1} = A.$

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Similar questions

Solve system of linear equations, using matrix method.
2x - y = -2
3x + 4y = 3
If $\text{A}=\text{diag}\begin{pmatrix}2&-5&9\end{pmatrix},\text{ B}=\text{diag}\begin{pmatrix}1&1&-4\end{pmatrix}$ and $\text{C}=\text{diag}\begin{pmatrix}-6&3&4\end{pmatrix},$ find.
$2\text{A}+3\text{B}-5\text{C}$
If a matrix has 8 elements, what are the possible orders it can have? What if it has 5 elements?
Find the values of k so that the function f is continuous at the indicated point:
$\text{f(x)}= \begin{cases}\text{k}\text{x}+1,\ \text{if}\ \text{x}\leq{\pi}\\ \cos\text{x}, \ \ \ \ \text{if}\ \text{x} >{\pi}\end{cases}$
$\text{at}\ \text{x} = {\pi}$
If the probability distribution of a random variable of X is given by
$X = x_i:$ 1 2 3 4
$P(X = x_i):$ 2k 4k 3k k
Write tyhe value of k.
If the vertices A, B and C of $\triangle\text{ABC}$ have position vectors (1, 2, 3), (-1, 0, 0) and (0, 1, 2), respectively, what is the magnitude of $\angle\text{ABC}?$
Find the angle between the line $\vec{\text{r}}=(2\hat{\text{i}}+3\hat{\text{j}}+9\hat{\text{k}})+\lambda(2\hat{\text{i}}+3\hat{\text{j}}+4\hat{\text{k}})$ and the plane $\vec{\text{r}}\cdot(\hat{\text{i}}+\hat{\text{j}}+\hat{\text{k}})=5$
If $A = [a_{ij}]$ is a skew-symmetric matrix, then write the value of $\sum_\text{i}\text{a}_\text{ij}.$
Evaluate the following integrals:$\int2\text{x}^3\text{e}^{\text{x}^{2}}\text{dx}$
Consider the binary operation $*$ and o defined by the following tables on set $S = \{a, b, c, d\}.$
$o$
$a$
$b$
$c$
$d$
$a$
$a$
$a$
$a$
$a$
$b$
$a$
$b$
$c$
$d$
$c$
$a$
$c$
$d$
$b$
$d$
$a$
$d$
$b$
$c$