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

$(y-3)^2$
Using the factoring of trinomials in the form $x^2+bx+c,$ the given expression, $y^2-6y+9 ,$ has $c$ equal to $9$ and $b$ equal to $-6 .$ The two numbers that give a product of $c$ and a sum of $b$ are $\{ -3,-3 \}.$ Hence, the factored form of the expression above is \begin{array}{l}\require{cancel} (y-3)(y-3) \\\\= (y-3)^2 .\end{array}