Factor: 81y^2 - 72y + 16.

1. Check that the first and last terms are perfect squares: 81y squared is (9y) squared, and 16 is 4 squared. 2. The middle term is negative, so the pattern to use is a squared - 2ab + b squared, which factors to (a - b) squared. 3. Check the middle term: twice the product of 9y and 4 is 72y, which matches the size of the middle term. 4. Write the square of the binomial: (9y - 4)(9y - 4), and check by multiplying: 81y squared - 36y - 36y + 16 gives back 81y squared - 72y + 16. _Source: OpenStax Elementary Algebra (CC BY 4.0), Ch 7 "Factoring", section 7.4 Factor Special Products_