In order to sum two polynomials, we need to group and add the like terms, i. e., terms for which the variable has the same exponent.
(8x³ + 3x - 2) + (9x² - 7 + 3x - 2x³)
= (8x³ - 2x³) + (9x²) + (3x + 3x) + (-2 - 7)
= (8 - 2)x³ + 9x² + (3 + 3)x - 9
= 6x³ + 9x² + 6x - 9
Therefore, adding those polynomials, we obtain:
6x³ + 9x² + 6x - 9
