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Old 04-21-2008, 10:46 PM   #1
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Join Date: Apr 2008
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Complex number modulus and the product of conjugates?

Hi,

I'm using barron's 2008 math 2 book to prepare for my iic. The typos in the "graphing complex numbers" section is absolutely killing me.

Questions:

Is the mod of a complex number the distance from the origin on the complex number plane? sqrt(a^2+b^2)

Are the graphs of conjugates the reflections across the x-axis (the book said y-axis :S )

Is the product of conjugates the square of the modulus? (a^2+b^2)

thanks!
kyoko is offline  
Old 04-22-2008, 12:24 AM   #2
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Okay, just so you know, that stuff will not show up on the Math II; the only time I've ever seen it is in my IB Math HL class.

The modulus of a +bi = |a + bi| = sqrt (a^2 + b^2) (that's just the way it's defined) And it is the distance from the origin to the point.

In terms of the graphs, the horizontal axis is your real component, while your vertical axis if your imaginary component.
If you have 3 - i and 3 + i, then they...hm, should be reflections across the x-axis I'm thinking...

(3 - i)(3 + i) = 9 - i^2 = 9 - (-1) = 9 + 1 = 10
|3 - i| = (3^2) + (-1)^2 = 9 + 1 = 10
So I would say yes, the product of conjugates is the square of the modulus.
CDN_dancer is offline  
Old 04-24-2008, 09:19 PM   #3
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Yea i checked with other sources and know for sure now Barron's book is wrong.

Thanks.
kyoko is offline  
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