Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

$225=5^2\times3^2$
The prime factorization of 225 can be calculated by dividing it with prime numbers: 225 is a multiple of 5. $225= 5\times45$ 45 is a multiple of 5. $225=5\times5\times9$ 9 is the square of 3. $225=5^2\times3^2$