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i² = −1, NOT +1

The most common CSCA complex-number mistake. When you expand and reach $i^{2}$, it becomes $-1$, not $+1$. The wrong-sign answer is always sitting in the options.

i2=−1(always)

Get this wrong, lose the question

i2

=−1

By definition of i

i3

=i2⋅i=−i

Multiply through

i4

=(i2)2=1

Powers cycle: i,−1,−i,1,…