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Thread: Complex Numbers Help

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    Complex Numbers Help

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    Re: Complex Numbers Help

    its an isoceles so you know that the other angles are 45 and 45, you do z1 - z2, then you rotate by 45 degree by multiply cis 45 then divide by root2 bc its shorter side of triangle then add it back to find z3, also do cis-45 and there should be 2 answers for z3
    Last edited by darkk_blu; 7 Feb 2018 at 10:34 PM. Reason: cant type complex yet

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    Re: Complex Numbers Help

    Eek I haven't done 4U in a while so I might be a bit rusty but this is what I got - hopefully it's right.

    https://i.imgur.com/a8xeaNY.jpg

    Essentially, since it's an isosceles triangle with z3 as a right angle, the remaining angles would be 45 degrees. Therefore, I think you can just manipulate the vector z1 and z2 by multiplying it with cis(pi/4) or cis (-pi/4) to eventually find z3.

    Hopefully the working out in the image makes sense.

    If I'm wrong let me know - I haven't done this in a while so I might've forgot some stuff.

    Also, I believe you can have two values of z3 I think - one above the real axis and one below the real axis. I'm not fully sure though.
    2017 HSC: Eng (Adv.) · 3U Math · 4U Math · Chem · Phys · Bio

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    Re: Complex Numbers Help

    Quote Originally Posted by captainhelium View Post
    Eek I haven't done 4U in a while so I might be a bit rusty but this is what I got - hopefully it's right.

    https://i.imgur.com/a8xeaNY.jpg

    Essentially, since it's an isosceles triangle with z3 as a right angle, the remaining angles would be 45 degrees. Therefore, I think you can just manipulate the vector z1 and z2 by multiplying it with cis(pi/4) or cis (-pi/4) to eventually find z3.

    Hopefully the working out in the image makes sense.

    If I'm wrong let me know - I haven't done this in a while so I might've forgot some stuff.

    Also, I believe you can have two values of z3 I think - one above the real axis and one below the real axis. I'm not fully sure though.
    Its wrong, but close. Check the moduli of the vectors, they don’t add up correctly, z1 to z2 is 5 but multiplying by Cis/4 only rotates it, it’s new moduli is also 5, which is incorrect, it should be shorter. I have the correct working out but can’t type it up until I get home, I’ll post again if I remember, the answer should be divided by sqrt2

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    water enthusiast captainhelium's Avatar
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    Re: Complex Numbers Help

    Quote Originally Posted by darkk_blu View Post
    Its wrong, but close. Check the moduli of the vectors, they don’t add up correctly, z1 to z2 is 5 but multiplying by Cis/4 only rotates it, it’s new moduli is also 5, which is incorrect, it should be shorter. I have the correct working out but can’t type it up until I get home, I’ll post again if I remember, the answer should be divided by sqrt2
    Ah yep that's true - silly mistake from me haha haven't done 4U in a while rip xD.

    Thanks for clearing that up!
    Last edited by captainhelium; 8 Feb 2018 at 5:33 PM.
    2017 HSC: Eng (Adv.) · 3U Math · 4U Math · Chem · Phys · Bio

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