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Maths help complex numbers

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The variable complex number z is given by z = 2cosθ + i(1 − 2 sinθ). Prove that the real part of 1/(z + 2 − i)
is constant for −π < θ < π.

I simplified the answer to (1/4)((cosθ +isinθ)/(1+cosθ)). Marking scheme says that real part equals 1/4. I thought that whatever is not multiplied with i is wholly the real part. Please explain why (1/4)(cosθ)/(1+cosθ) is not correct.
 
Messages
10
Reaction score
3
Points
13
The variable complex number z is given by z = 2cosθ + i(1 − 2 sinθ). Prove that the real part of 1/(z + 2 − i)
is constant for −π < θ < π.

I simplified the answer to (1/4)((cosθ +isinθ)/(1+cosθ)). Marking scheme says that real part equals 1/4. I thought that whatever is not multiplied with i is wholly the real part. Please explain why (1/4)(cosθ)/(1+cosθ) is not correct.
 

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