Surd:- If n is a positive integer ( n>1 ) and a rational number a (>0) isnot the nthpower of any rational number, then is called a surd of nth order.

If a is a positive rational number which can not be expressed as the nth power some rational number, then the rational number is called a surd or radical .

The symbol is called radical sign,

n is called the order of the surd ( or radical ) and a is called radicand.