11x³ – 8y² + 2x³ + 8y² = (11x³ + 2x³) + (-8y² + 8y²) = 13x³ + 0 = 13x³
7,2x³ + 0,8y – 1,2x³ + 2,2y = (7,2x³ - 1,2x³) + (0,8y + 2,2y) = 6x³ + 3y = 6x³ + 3y
4mn³ – 5mn + 2m²n³ + mn³ - mn - 2m²n³ = (4mn³ + mn³) + (-5mn - mn) + (2m²n³ - 2m²n³) = 5mn³ - 6mn + 0 = 5mn³ - 6mn
c³d + cd + cd³ – 3c³d – cd – 3cd³ = (c³d – 3c³d) + (cd - cd) + (cd³ – 3cd³) = -2c³d + 0 + (-2cd³) = -2c³d - 2cd³