Step-by-step explanation:
[tex] = {i}^{31} [/tex]
[tex] = {i}^{28} \times {i}^{3} [/tex]
[tex] = {( {i}^{4} )}^{7} \times ( {i}^{2} \times i)[/tex]
[tex] = ( {i}^{2} \times {i}^{2} ) {}^{7} \times {i}^{2} \times i[/tex]
[tex] = ( - 1 \times ( - 1)) {}^{7} \times ( - 1) \times i[/tex]
[tex] = {1}^{7} \times ( - i)[/tex]
[tex] = 1 \times ( - i)[/tex]
[tex] = - i[/tex]
The answer is D.
