Here's one way to think about it. It's not really the standard way though, so if you start reading it and it just confuses you, then just ignore it.

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Take your finger and point to the right. This is "1".

Rotate your finger 90 degrees counterclockwise. This rotation is multiplying by "i". Your finger should be pointing straight up, which is 1*i = i.

Rotate your finger 90 degrees counterclockwise again. This is multiplying by "i" again, so we are now at

i*i = i^2.

Your finger should be pointing to the left, which is the opposite direction from "1", so it should be "-1". We have just shown that

i^2 = -1.

Now, since

i^2 = -1,

we can take square roots to get

i = √(-1)

by definition, i = √(-1)

therefore i² = (√(-1))(√(-1)) = -1

x = i is one of the two roots of the parabola y = x² + 1. The other is -i.

It is where the parabola would cross the x-axis if the x-axis were an imaginary one.