Question

1. (9r³ + 5r² + 11r)+(-2r³ + 9r - 8r²)

Explanation:

Step1: Combine like - terms of $r^3$

$(9r^3-2r^3)+(5r^2 - 8r^2)+11r + 9r$
$=7r^3+(5r^2 - 8r^2)+11r + 9r$

Step2: Combine like - terms of $r^2$

$7r^3-3r^2+11r + 9r$

Step3: Combine like - terms of $r$

$7r^3-3r^2+(11r + 9r)$
$=7r^3-3r^2 + 20r$

Answer:

$7r^3-3r^2 + 20r$