According to the formula:

i^(4n)= 1

i^(4n+ 1)=i

i^(4n+2)=- 1

i^(4n+3)=-i

You can know:

i^ 165=i^(4*4 1+ 1)=i

i^200=i^(4*50)= 1

i^278=i^(4*69+2)=- 1

Thank you. You can ask if you don't understand.

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