Surds:You can't write root 15 exactly as a decimal. It is called a surd.root ab = root a x root b
Rationalizing the denominator of a fraction means making the denominator a whole number. You can do it by multiplying the top and bottom numbers by the surd part.
Factors and Primes:Prime numbers are numbers which are only divisible by them self and one.2 is the only EVEN prime number1 IS NOT a prime number