1. Extract the square root of the first term
2. The second term is the product of the first term and the last term multiplied by constant 2.
10s / 2 = 5s = the first and last terms are s and 5 (respectively)
3. Extract the square root of the last term
Therefore, the square of a binomial factor of s^2+10s+25 is (s+5)^2.