Question 1207479
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<pre>

arg(z1*z2) is always equal to arg(z1) + arg(z2)    (by the modulo of {{{2pi}}}).



From the other side, if  |z1| = |z2|,  then arg(z1+z2) = {{{(arg(z1)+arg(2))/2}}} 

according to the parallelogram rule of adding vectors (= complex numbers), which

is in this case the "rhombus" rule of adding vectors.



From this, we conclude that, under given conditions,

    arg(z1*z2) = arg(z1) + arg(z2) = {{{2*((arg(z1) + arg(z2))/2)}}} = 2*arg(z1+z2) = {{{2*(pi/4)}}} = {{{pi/2}}}.    <U>ANSWER</U>
</pre>

Solved.