Give an example of an irrational number and how you mat use it or come across in the real world.

An irrational number is any real  number which can not be
expressed in the form of p/q , where p and q are integers.The irrational are many and
uncountable.

Some examples: e, pi and
sqrt19.

We know e = Lt (1+1/x)^x as n--> infinity.
The value of e is like 2.71828...

We know pi = Length of
circumference of a circle/length of diameter of that circle. the value of pi is like
3.14159...

Square root 19. The value we know is between 4
and 5.

The knowledge of pi  is essential in geometry. It is
used to know the length of circumference given the radius or
diameter.

Rather than use , the invention of irrational
number has contributed to the completeness of the idea of numbers. It gave a sense of
enlightement that between any two distinct perfect square roots , there are still more
square roots which need not be in p/q form alone.