Which methods of factoring do you use to factor completely?
You (try to) divide your number by successive primes
Say you want to factor
Even number, divide by 2:
Even, divide by 2:
Odd, so try 3:
7 is a prime, so you're finished.
You write the result as
You never have to try a prime that is larger than the square root of the number left, because if that would divide evenly, the result is a smaller number, and you would have already tried that.