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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.

S_{11}= 0.894 [itex]\angle[/itex] -60.6

S_{21}= 3.122 [itex]\angle[/itex] 123.6

S_{12}= 0.020 [itex]\angle[/itex] 62.4

S_{22}= 0.781 [itex]\angle[/itex] -27.6

Then, how does |Δ| = |S_{11}S_{22}- S_{12}S_{21}| = |0.696 [itex]\angle[/itex] -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

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# Multiplying and subtracting coordinates

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