Out of the four trinomials, y^2+18y+81 is correct. Step By Step Answer: To determine a perfect square trinomial, the first and third terms have to be square roots and the middle term has to be two times the square root of the third term.
y^2 is a square root and 81 is a square root. y^2 simplifies to y and 81 simplifies to 9. It would be y+18y+9 The third term is 9, so multiply that by two and you get 18! Therefore, that is correct! y^2+18y+81 is a perfect square trinomial!