= Solution
Take the two interfering <complex amplitudes> to have equal intensities $I_0/2$ and relative <phase> $kx$. The <interference> cross term then gives
$$
I=\frac{I_0}{2}+\frac{I_0}{2}+2\sqrt{\frac{I_0}{2}\frac{I_0}{2}}\cos(kx)
=\boxed{I_0[1+\operatorname{Re}(e^{ikx})]}.
$$
Thus the mean intensity is $I_0$, the maximum is $2I_0$, and the minima are
$$
\boxed{x=(m+\tfrac12)\lambda},\qquad m\in\mathbb Z.
$$
The <optical path difference> period is $\lambda$ and the mirror-displacement period is $\lambda/2$. The assumed equal intensities refer to the two fields at the chosen output, with matching <polarization of waves> and full <optical coherence>. They set the normalization; they should not additionally be interpreted as all incident light entering that output port. A physical lossless <Michelson interferometer> has a complementary second output.
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