Answer:
[tex]- {t}^{4} + 4 {t}^{3} - 7 {t}^{2} - 1[/tex]
Step-by-step explanation:
[tex] ( - {t}^{4} - 5 {t}^{3} - 10 {t}^{2} ) + (9 {t}^{3} + 3 {t}^{2} - 1) \\ = - {t}^{4} - 5 {t}^{3} - 10 {t}^{2} + 9 {t}^{3} + 3 {t}^{2} - 1 \\ = - {t}^{4} + 9 {t}^{3}- 5 {t}^{3} + 3 {t}^{2} - 10{t}^{2} - 1 \\ = - {t}^{4} + 4 {t}^{3} - 7 {t}^{2} - 1[/tex]
