Do -3 and -5 correctly factor the trinomial y^2 - 6y + 15 into (y-3)(y-5)?

1. The two numbers must multiply to 15 and add to -6 to factor the trinomial as (y + m)(y + n). 2. The factor pair -3 and -5 does multiply to positive 15, since a negative times a negative is positive. 3. But -3 plus -5 equals -8, not the -6 needed for the middle term. 4. The other factor pair of 15, which is -1 and -15, adds to -16 and is even further off, so no integer pair works and the trinomial is prime. _Source: OpenStax Elementary Algebra (CC BY 4.0), Ch 7 "Factoring", section 7.2 Factor Quadratic Trinomials with Leading Coefficient 1_