Saturday, June 25, 2016

analysis - what are real and imaginary part of this expression



I have M:=a(b+ic)de and all variables a,b,c,d,e are real. Now I am looking for the real and imaginary part of this, but this square root makes it kind of hard.



Answer



a(b+ic)de=adeb+ic



Let b+ic=x+iy



b+ic=(x+iy)2=x2y2+2xyi



Equating the real & the imaginary parts, b=x2y2,c=2xy



So, b2+c2=(x2y2)2+(2xy)2=(x2+y2)2x2+y2=b2+c2




We have x2y2=b



2x2=b2+c2+bx2=b2+c2+b2


x=±b2+c2+b2



and y2=x2b=b2+c2b2



y=±b2+c2b2




Now, the sign of y= sign of x sign of c


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