anonymous
  • anonymous
How to find prove that the complex conjugate of Z(with a line over it)^2 is not the same as Z^2(with a line over it)?
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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schrodinger
  • schrodinger
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asnaseer
  • asnaseer
If you write the complex number z as:\[z=a+ib\]Then do you know what \(\bar{z}\) equals in terms a and b?
anonymous
  • anonymous
i know that z=a+bi, and z(line over)=a-bi, but when i squared the first one i got (a^2-b^2)-2abi and i got the same thing when i solve (a+bi)^2(all with a line over it)
asnaseer
  • asnaseer
\[(a+ib)^2=(a+ib)(a+ib)=a^2+2abi+i^2b^2=a^2+2abi-b^2=a^2-b^2+2abi\]

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asnaseer
  • asnaseer
That last term is:\[=a^2-b^2+2abi\]
anonymous
  • anonymous
yeah i got that part... that's the z^2 part right? because after that the problem wants z^2(with a line over z^2)
asnaseer
  • asnaseer
yes, so now find \(\bar{z}^2\) using the same technique, i.e.:\[\bar{z}^2=(a-ib)^2=(a-ib)(a-ib)=?\]
anonymous
  • anonymous
i did that and i got a^2-b^2-2abi... so this is the first part of the problem that i have to compare to z^2(with a line over the entire thing including the square... look at the attatched picture, im not sure if I'm typing it right, but this is the question at the top there:
asnaseer
  • asnaseer
So is this the question - prove that:\[(\bar{z})^2\ne\bar{(z^2)}\]
anonymous
  • anonymous
yes
asnaseer
  • asnaseer
ok, then steps are: 1. set z = a + bi 2. find \(z^2\) using this 3. take the complex conjugate of this expression 4. set \(\bar{z}\)=a=bi 5. find \(\bar{z}^2\) using this 6. compare the two results
anonymous
  • anonymous
for step 3, would the complex conjugate of z^2 be a^2-b^2-2abi?
asnaseer
  • asnaseer
yes
anonymous
  • anonymous
then isn't it the same as the other result? i got a^2-b^2-2abi as the complex conjugate squared [z^2(with a line over it)] as well
asnaseer
  • asnaseer
yes - so do I. Are you 100% sure you have the correct question?
anonymous
  • anonymous
not 100%... it was from a test that we started today and are finishing tomorrow. I remember the z terms correctly but im not exactly sure what it was asking... i guess maybe the question was to prove that they ARe the same?
asnaseer
  • asnaseer
yes - that is what I believe the question would have stated
hartnn
  • hartnn
question is correct, they are not same
anonymous
  • anonymous
hartnn- how are they not the same?
asnaseer
  • asnaseer
@hartnn - the /revised/ question is: \[(\bar{z})^2\ne\bar{(z^2)}\]
hartnn
  • hartnn
{z(bar) }^2 = left side = (a-bi)(a-bi)
hartnn
  • hartnn
right side =conjugate of (a+bi)(a+bi)
asnaseer
  • asnaseer
correct - and they both work out to be the same value
hartnn
  • hartnn
oh dear, sorry, i worked out right side incorrectly
asnaseer
  • asnaseer
so I believe the question should have been: Prove that \((\bar{z})^2=\bar{(z^2)}\)
anonymous
  • anonymous
yes i beleive that was the question. okay, thanks for all your help!
asnaseer
  • asnaseer
yw :)

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