Question

Represent the following sets in set-builder form
(i) $X=$ { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday , Saturday}
(ii) $A=\{1,\frac{1}{2},\frac{1}{3},\frac{1}{4},\frac{1}{5},...\}$

Answer 1

(i) $X=$ { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday , Saturday}
The set $X$ contains all the days of a week.
Hence in set builder form, we write
$X=$ { $x:x$ is a day in a week }
(ii) $A=\{1,\frac{1}{2},\frac{1}{3},\frac{1}{4},\frac{1}{5},...\}$. The denominators of the elements are $1,2,3,4,...$
$\therefore$ The set-builder form is $A=\{x:x=\frac{1}{n},n\in N\}$