a)
[tex]( - 7 {)}^{9} \times ( - 7 {)}^{6} \times ( - 7 {)}^{5} = ( 7 {)}^{20} \boxed{ \large{( +)}}[/tex]
b)
[tex]( - 4 {)}^{16} \times {4}^{8} \times ( - 4 {)}^{0} = {4}^{24} \boxed{\large{ ( + )}}[/tex]
c)
[tex] \frac{( - 3 {)}^{13} }{ {3}^{2} \times ( - 3 {)}^{1} } = \frac{( - 3 {)}^{13} }{ ( - 3 {)}^{3} } = {3}^{10} \boxed{\large{ ( + )}}[/tex]
