Gujarat BoardEnglish MediumSTD 11 ScienceMATHSSets1 Mark
Question
If A is any set, prove that: $\text{A}\subseteq\phi\Leftrightarrow\text{A}=\phi.$
✓
Answer
The symbol '⇔' stands for if and only if (in short if). In order to show that 2 sets A and B are equel we show htat $\text{A}\subseteq\text{B}$ and $\text{B}\subseteq\text{A}.$ We have $\text{A}\subseteq\phi.\ \because \phi$ is a subset of every set $\therefore\ \phi\subset\text{A}$ Hence $\text{A} =\phi$ To show the backward implication, suppose that $\text{A}= \phi$ $\because$ Every set is a subset of itself. $\therefore\ \phi=\text{A}\subseteq \phi$ Hence, proved.
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