Angle notation addition - numerical addition problem

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Et Tu, Brute?
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This is a problem I've come across in my engineering course, but the problem is purely mathematical. But for reference, it is related to calculating parallel impedance (hence the product over sum) using angle notation.

I've attached the problem I'm having, it is from my lecture notes, no idea how he has got the values on the denominator. I thought it was from the cosine/sine rules as I referenced this webpage initially on how to do it (though the example is a right angle, hence I used cosine/sine rules) http://www.allaboutcircuits.com/text...ctor-addition/

My problem/working is attached below. Note the triangle etc was all my working, all I have from the question is the first part, I assumed I needed to use cosine/sine rules and seems like I am wrong.
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Et Tu, Brute?
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And if you need to zoom in, right click open image in new tab and you can zoom in a lot from there.
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DFranklin
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Do you know how to convert from polar to Cartesian coordinates and vice versa?
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Et Tu, Brute?
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(Original post by DFranklin)
Do you know how to convert from polar to Cartesian coordinates and vice versa?
yeah kind of. Haven't done it for a while, but I've done it before.
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DFranklin
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(Original post by Et Tu, Brute?)
yeah kind of. Haven't done it for a while, but I've done it before.
Well, your vectors are in polar coordinates. You need to convert to Cartesian, add the Cartesian coordinates, and then convert back.
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Et Tu, Brute?
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(Original post by DFranklin)
Well, your vectors are in polar coordinates. You need to convert to Cartesian, add the Cartesian coordinates, and then convert back.
ok, so I have

1)x = 300cos(0) ; y = j300sin(0)
x = 300; y=0

2)x = 282.8cos(-45); y=j282.8sin(-45)
x= 199.97; y=-j199.97

So what from here?

(300+199.97) - j199.97
= 499.97 -j199.97

got it, now:
sqrt(500^2+200^2) ~538


Thanks for the help!
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