Prime Factors

What are they?

All composite numbers can be written as the product of prime numbers. This product is known as the prime factorisation of that number.

Example

The prime factorisation of 12 is 2x2x3

The prime factorisation of 42 is 2x3x7

How to find prime factors

To find the prime factorisation of 45, start by finding a factor of 45 that is also a prime number. The write 45 as a product.

45=5x9If the last number is not prime then repeat the process until 45 is written as a product of primes.

45=5x3x3

Example

Find the prime factorisation of 120.120 =2x60

=2x2x30=2x2x2x15=2x2x2x3x5

So 120=2x2x2x3x5.