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# Complex Number Proof watch

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1. Need help with a proof question.

Let z and w be complex numbers and show that:

mod(z+w)^2 - mod(z-W)^2 = 4Re(z)Re(w)

Where W is the complex conjugate of w. I didn't know how to place the bar above the w on here.

I tried to do it by setting z = a+ib, w = c+id, W = c-id, but not sure if this is write.

Any help much appreciated.
2. (Original post by IceCityRabz)
Need help with a proof question.

Let z and w be complex numbers and show that:

mod(z+w)^2 - mod(z-W)^2 = 4Re(z)Re(w)

Where W is the complex conjugate of w. I didn't know how to place the bar above the w on here.

I tried to do it by setting z = a+ib, w = c+id, W = c-id, but not sure if this is write.

Any help much appreciated.
I would do it the way you're doing it so just continue and eventually you should get two expressions, one for LHS and one for RHS which are the same.

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