# Physics Cup – TalTech 2021 – Pr. 2, Hint 3.

Continuing with the hint No 2, it is useful to notice that if $z$ in the expression $\varepsilon = \mathrm e^{\mathrm i \varphi} + z$ corresponds to $\vec l \times \vec v_2$ then $\vec l \times \vec v_1$ is obtained by making $z$ two times bigger and rotating by 90 degrees which is the same as multiplying by the imaginary unit, hence what we need is $2z\mathrm i$. From here, the full solution is just a few lines away.
NB! This is the last hint, the final deadline for submitting solutions of Problem 2 is 6th March, 23:59 GMT!

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