Question

The cardinality of set $A=\left\{\right(a,b):ab=36\text{where}a\text{and}b\text{are coprime to each other}\}$ is

Answer 1

Factors of $36$ are $\{1,2,3,4,6,9,12,18,36\}$
$a,b$ are coprime
So, possible pairs are
$(1,36),(4,9),(9,4),(36,1)$
$A=\left\{\right(1,36),(4,9),(9,4),(36,1\left)\right\}$
Cardinality of $A$ is $4$