Irrational Number Importent Definitions Chapter 1 Maths Class 9 Notes Chapter 1 Number System Maths Class 9 NCERT

Irrational number :-
Numbers that cannot be put in the form of p/q , where q is not equal to 0
When p and q both are integers
Example  √2  , √5 and √8 etc
Every fraction is a rational number but a fraction need not be a rational number.
Standard form of rational number :-
A rational number is said to be in the standard form if q is positive integer and the integers p and q have no common divisor other than 1.
Example 2/5 , 7/9 etc
We can find as many rational numbers between x and y using the formula (x+y)/2
If x and y are any two rational numbers, then :
Sum or difference of two x and y will always rational
And product or division of x and y will always rational
If  one variable is rational and other is irrational  in x and y then
Sum or difference of two x and y will always irrational
And product or division of x and y will always irrational