::Let 1 - a = b < 0. Then <math>\gamma = \frac{1}{\sqrt{b}} = \frac{1}{z}</math> where <math>z = x + iy</math> is an arbitrary complex number, with <math>i = \sqrt{-1}</math>, i.e. the "imaginary number."
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::Let <math>1 - a = b < 0</math>. Then <math>\gamma = \frac{1}{\sqrt{b}} = \frac{1}{z}</math> where <math>z = x + iy</math> is an arbitrary complex number, with <math>i = \sqrt{-1}</math>, i.e. the "imaginary number."
In other words, the Lorentz factor would involve an imaginary number.
In other words, the Lorentz factor would involve an imaginary number.