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# i as the principal root of -1

The formal definition of i is i^2=-1 and

*√-1=i, and there's a good reason for this (although it's a bit technical). See Sal explain why. Created by Sal Khan.***not**If you're seeing this message, it means we're having trouble loading external resources for Khan Academy.

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# i as the principal root of -1

Current time:0:00Total duration:6:44

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The formal definition of i is i^2=-1 and **not **√-1=i, and there's a good reason for this (although it's a bit technical). See Sal explain why. Created by Sal Khan.