Suppose the mirrors in a Michelson interferometer are perfectly aligned and the path lengths to mirrors $\mathrm{M}_{1}$ and $\mathrm{M}_{2}$ are identical. With these initial conditions, an observer sees a bright maximum at the center of the viewing area. Now one of the mirrors is moved a distance $x .$ Determine $a$ formula for the intensity at the center of the viewing area as a function of $x$, the distance the movable mirror is moved from the initial position.