The numbers that can be expressed in the form of a fraction are called rational numbers. While that numbers that cannot be expressed in the form of a fraction are called irrational numbers.
[tex]\sqrt{45} =\sqrt{3 \times 3 \times 5}[/tex]
[tex]\sqrt{45} =3\sqrt{5}[/tex]
[tex]3\sqrt{5}[/tex] is an irrational number, it cannot be expressed in the form of a fraction.
