Resposta :
[tex]c)(5 {x}^{2} + 2x - 4) - (6 {x}^{2} - x + 7) = \\ 5 {x}^{2} + 2x - 4 - 6 {x}^{2} + x - 7 \\ - {x}^{2} + 3x - 11[/tex]
[tex]d)(9a - 8b - c) + ( - 2a + 6b + 7c) = \\ 9a - 8b - c - 2a + 6b + 7c \\ 7a - 2b + 6c[/tex]
[tex]c)(5 {x}^{2} + 2x - 4) - (6 {x}^{2} - x + 7) = \\ 5 {x}^{2} + 2x - 4 - 6 {x}^{2} + x - 7 \\ - {x}^{2} + 3x - 11[/tex]
[tex]d)(9a - 8b - c) + ( - 2a + 6b + 7c) = \\ 9a - 8b - c - 2a + 6b + 7c \\ 7a - 2b + 6c[/tex]