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Im having a bit of trouble with a question. I have to convert:

[tex]Ke^{j\delta} - Ke^{j\psi}[/tex]

Into the form

[tex]re^{j\theta}[/tex]

This is the second part of the question, the first part was an addition instead of subtraction which i managed by using this formula:

[tex]z_1 + z_2 = K(e^{j\delta} + e^{j\psi}) = Ke^{j(\delta + \psi)/2}(e^{j(\delta - \psi)/2} + e^{-j(\delta - \psi)/2}) = 2K\cos((\delta - \psi)/2).e^{j(\delta + \psi)/2}[/tex]

I cant really see where to go with the subtraction though...is it maybe to do with a sin rule? To be honest i dont fully understand the formula above but it was given to us...Ive fiddled around with the maths for a while but its totally headbanging :( Hoping someone can help!