Answer:
1 - i
Step-by-step explanation:
[tex] {i}^{19} + {i}^{20} \\ \\ = {i}^{18} .i + {i}^{20} \\ \\ = {( {i}^{2} )}^{9} .i + {( {i}^{2} )}^{10} \\ \\ = {( - 1)}^{9} .i + {( - 1)}^{10} \ \\ ( \because \: {i}^{2} = - 1) \\ \\ ( - 1).i + 1 \\ \\ = - i + 1 \\ \\ = 1 - i[/tex]
