5. Привести подобные члены: 1) 11x³ - 8y² + 2x³ + 8y²; 2) 7,2x³ + 0,8y - 1,2x³ + 2,2y 3) 4mn³ - 5mn + 2m²n³ + mn³ - mn - 2m²n³; 4) c³d + cd + cd³ - 3c³d - cd - 3cd³.

Решение:

1. \(11x^3 - 8y^2 + 2x^3 + 8y^2 = (11x^3 + 2x^3) + (-8y^2 + 8y^2) = 13x^3 + 0 = 13x^3\)
2. \(7.2x^3 + 0.8y - 1.2x^3 + 2.2y = (7.2x^3 - 1.2x^3) + (0.8y + 2.2y) = 6x^3 + 3y\)
3. \(4mn^3 - 5mn + 2m^2n^3 + mn^3 - mn - 2m^2n^3 = (2m^2n^3 - 2m^2n^3) + (4mn^3 + mn^3) + (-5mn - mn) = 0 + 5mn^3 - 6mn = 5mn^3 - 6mn\)
4. \(c^3d + cd + cd^3 - 3c^3d - cd - 3cd^3 = (c^3d - 3c^3d) + (cd - cd) + (cd^3 - 3cd^3) = -2c^3d + 0 - 2cd^3 = -2c^3d - 2cd^3\)

Ответ: 1) \(13x^3\); 2) \(6x^3 + 3y\); 3) \(5mn^3 - 6mn\); 4) \(-2c^3d - 2cd^3\).