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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_radius_normal(lat_radians: float, ell: Ellipsoid = None) -> float: """ Compute normal radius of planetary body Parameters lat_radians : float latitude in radians ell : Ellipsoid, optional reference ellipsoid Returns ------- radius : float normal radius (meters) """

    if ell is None:
        ell = Ellipsoid()

    a = ell.a
    b = ell.b

    return a**2 / sqrt(a**2 * cos(lat_radians)**2 + b**2 * sin(lat_radians)**2)