An approximate solution to a problem is a solution that has been rounded to a limited number of digits.
An irrational number is a number that can not be expressed exactly as the quotient of two integers.
A perfect square is a number whose square root is an integer.
principal square root
The principal square root is the positive square root of a number, to distinguish it from the negative value. 3 is the principal square root of 9; -3 is also a square root of 9, but it is not principal square root.
Differentiate between rational and irrational numbers and classify real numbers.