Thu gọn đa thức: P(y) = -2y^3 + y + 11/7 y^3 + 3y^2 - 5 - 6y^2 + 9.

P(y) = -2y³ + y + $\frac{11}{7}$y³ + 3y² - 5 - 6y² + 9

P(y) = (-2y³ + $\frac{11}{7}$y³) + (3y² - 6y²) + y + (- 5 + 9)

P(y) = $\left(\frac{-14}{7}{y}^3+\frac{11}{7}{y}^3\right)$ + (-3y²) + y + 4

P(y) = $\frac{-3}{7}$y³ - 3y² + y + 4.

Vậy P(y) = $\frac{-3}{7}$y³ - 3y² + y + 4.