# Multiplying and subtracting coordinates

1. Feb 4, 2012

### OnceMore

Hello,

I am hoping someone can help me understand a problem in a text book. It just assumes you know how to do a littel bit of maths, which I don't, and haven't been able to figure out.

S11 = 0.894 $\angle$ -60.6
S21 = 3.122 $\angle$ 123.6
S12 = 0.020 $\angle$ 62.4
S22 = 0.781 $\angle$ -27.6

Then, how does |Δ| = |S11 S22 - S12 S21| = |0.696 $\angle$ -83|

I have tried different things, for example, converting between cartesian and polar etc, but nothing seems to get me there.

Multiplying the respective r parts, and subtracting as needed seemed to get me close there, but doing the same with the angles didn't work out.

Thanks.

-S

2. Feb 4, 2012

### OnceMore

Oh, sorry ....I just figured it out!

Taking a break and coming back to it does help.

....just a thought, should I explain how it is done in case anyone else is looking to know this sort of thing?

I don't know what the protocol would be on that.

Slán
-S