So, let's start out with what the definition of complex number is.

J is equal to the square root of minus 1.

A lot of other applications,

especially in math, they use i to represent the square root of minus 1.

We use J in electrical engineering because we tend to use i for current.

So J is equal to the square root of minus 1.

That means J square is equal to minus 1.

Now, we're going to see 1 over J come up a lot, so

we want to find a simple form for that.

So 1 over J, we can actually come up with a way of simplifying this.

I'm going to multiply by j over j.

That gives me j in the numerator and j squared in the denominator.

Well that equals -1.

So this comes out to -j.

So, as something off to the side, I'll write this as 1/j = -j.

We use this a lot, so remember that.